I love me some Borderlands. I am about 3 Achievements shy from S ranking it, including Moxxi's Underdome. (shudder) I have put in an obscene amount of time into it, second only to maybe the Mass effect series. I love the just fucking ridiculousness of it, that vast range of shit to go find, and the unprecedented loot whoring.
 
But man, it needs some work still. There are still some really annoying bugs to be found; online play is a coin toss that someone won't break it  with modded weapons, or steal the good shit; and there are just some head scratching exclusions. So here is my quick and dirty list of things I would kill to have fixed in the last patch/DLC, or in the Sequel.
 

1. Add fast-travel to the DLC, specifically Knoxx. Knoxx is HUGE, and has lts of roads and stuff, and even has the new vehicles, but when you just want to pop in and run Crawmerax, or the Armory, you have to slog through map, after map to get there. I don't know if there is a tech limitation that needs to overcome, or a stupid design decision, but it needs done.
2. On that note, travel itself could be juiced up. I would really like the map screen have more options, including setting waypoints, and flipping to other pages, so you can see where you are going. 
3. Add more guns. Better guns.
   
4. Fix rocket launchers. They are next to useless with some classes. And they are so finicky with how they deal damage and splash damage. And add some guided or homing rockets.
5. FIX UNDERDOME, you fucks. And send us an apology. Add checkpoints. Add weapon proficiency increases, or drops for the creeps.
6. Just give it another bug sweep.
7. Edited to Add...
   
8. Gatling guns.
9. Ice or Temporal elements and abilities. Sometimes i really just want to slow the mobs down a bit, THEN mow them down
10. Give us a claptrap! Give us a companion fellow that you can give vender junk to, who will go and sell stuff, like the dog from Torchlight. Or a grinder like Deathspank.
    

• More story, better story, actually have a real story. Seem to be a sticking point.
  
• Crafting is another big one. Being able to take that big badass gun, and make it set stuff on fire, or add a scope to that one almost great gun... If you could break down all the vender trash and recycle the parts, it would make grinding a little more fun.
• A trade system. @ Brackynews  had the great idea of mailboxes so you could send gear to either your other characters, or your friends. its not like there aren't a crapload of mailboxes in the game already...
• Horizontal splitscreen, please fuck.
• Custom characters, more classes, more trees, more special abilities. 
• Armor as well as shields.
• Suppressed weapons for stealth killing, and better AI reactions to such. Actually just better AI than just constantly run at and/or shoot at you and yell.
• "A minimap, for fucks sake".
• MOREDERLANDS, AMIRITE?
• Remove dueling, its borken and never works as it should.
• Add Knoxx vehicles to vanilla game worlds.
• Address coop quest system issues
• Some randomization to some areas.
  

I love me some Borderlands. I am about 3 Achievements shy from S ranking it, including Moxxi's Underdome. (shudder) I have put in an obscene amount of time into it, second only to maybe the Mass effect series. I love the just fucking ridiculousness of it, that vast range of shit to go find, and the unprecedented loot whoring.
 
But man, it needs some work still. There are still some really annoying bugs to be found; online play is a coin toss that someone won't break it  with modded weapons, or steal the good shit; and there are just some head scratching exclusions. So here is my quick and dirty list of things I would kill to have fixed in the last patch/DLC, or in the Sequel.
 

1. Add fast-travel to the DLC, specifically Knoxx. Knoxx is HUGE, and has lts of roads and stuff, and even has the new vehicles, but when you just want to pop in and run Crawmerax, or the Armory, you have to slog through map, after map to get there. I don't know if there is a tech limitation that needs to overcome, or a stupid design decision, but it needs done.
2. On that note, travel itself could be juiced up. I would really like the map screen have more options, including setting waypoints, and flipping to other pages, so you can see where you are going. 
3. Add more guns. Better guns.
   
4. Fix rocket launchers. They are next to useless with some classes. And they are so finicky with how they deal damage and splash damage. And add some guided or homing rockets.
5. FIX UNDERDOME, you fucks. And send us an apology. Add checkpoints. Add weapon proficiency increases, or drops for the creeps.
6. Just give it another bug sweep.
7. Edited to Add...
   
8. Gatling guns.
9. Ice or Temporal elements and abilities. Sometimes i really just want to slow the mobs down a bit, THEN mow them down
10. Give us a claptrap! Give us a companion fellow that you can give vender junk to, who will go and sell stuff, like the dog from Torchlight. Or a grinder like Deathspank.
    

• More story, better story, actually have a real story. Seem to be a sticking point.
  
• Crafting is another big one. Being able to take that big badass gun, and make it set stuff on fire, or add a scope to that one almost great gun... If you could break down all the vender trash and recycle the parts, it would make grinding a little more fun.
• A trade system. @ Brackynews  had the great idea of mailboxes so you could send gear to either your other characters, or your friends. its not like there aren't a crapload of mailboxes in the game already...
• Horizontal splitscreen, please fuck.
• Custom characters, more classes, more trees, more special abilities. 
• Armor as well as shields.
• Suppressed weapons for stealth killing, and better AI reactions to such. Actually just better AI than just constantly run at and/or shoot at you and yell.
• "A minimap, for fucks sake".
• MOREDERLANDS, AMIRITE?
• Remove dueling, its borken and never works as it should.
• Add Knoxx vehicles to vanilla game worlds.
• Address coop quest system issues
• Some randomization to some areas.
  

I think the sequel needs an actual story.

All I want from a Borderlands sequel is that it is called Morederlands.

Needs more Mad Moxxi.
 
Love that crazy bitch!

Who knows? They might fix all of that soon.  
 
As far as guns go, there are a shit ton of guns. You sound as if you've collected every gun already.

For the next game: 

• Trade system     
• Crafting System + The ability to modify guns (class specific. For example, the hunter can only change snipers and revolvers)   
• Crazier abilities     
• A story that makes sense but is as light hearted and fun as the first Borderlands

How about an actual story?

 I'd like more equipment/armor type items and more classes. Or perhaps just more specialized classes.

How about Horizontal splitscreen? And while they're at it how about not having the inventory/mission screen be bigger than the splitscreen so it cuts it off on either side?

" Who knows? They might fix all of that soon.   As far as guns go, there are a shit ton of guns. You sound as if you've collected every gun already. "

" I agree with you on the Rocket Launchers. They are worthless. Add more guns Huh? They had over two million guns. Underdome sucked it is unfixable. Maybe not wait a year for the final DLC too? "

" @Axxol said:

" Who knows? They might fix all of that soon.   As far as guns go, there are a shit ton of guns. You sound as if you've collected every gun already. "

I haven't collected every gun, but have gotten soooo much vender trash its not even funny. "

You do not get to open the vault.   WTF

-Make modding a thing of the past.  It's just no fun playing with 3 level 70s with modded shotguns and shields.
-FIx the online coop in general, so after I leave a random game, my quest log isn't full of quests I haven't started yet.  Somehow the questing during online needs to be fixed.  I wasn't crazy about the way it was set up now.
And that's really the only problems I had, beside ones you mentioned.

I think it should have a way better story. The shooting was very enjoyable but the ending of the game sucked big time!

The lack of fast travel in Knoxx pissed me off so much. It was a hassle to try and get anywhere past T-Bone Junction. The rest of your issues...they dont really bother me. I never play splitscreen and there are soooo many guns I havent found yet. I also didnt even bother with The Underdome after I heard how batshit insane it was

I agree, for as good as Borderlands is, it needs a lot of tweaking:

• Overhaul (or just remove) the "dueling" system. It simply doesn't work, one guy is automatically going to waste the other, even if they're only a few levels different. It's not fun, it's not rewarding.
• More character classes, more customization options. Basically I'd like a character creator, I hate how everyone looks the same. Also have a more branching skill tree.
  
• Would be cool to be able to build your own weapons too, somehow make it based on materials/items you find, and have an upgradable skill that lets you craft/enhance weapons.
• Bigger/better boss battles. This had one of the lamest end bosses EVER.
  

I want a shit load of different armour and more diverse characters.

• I would pay $7 for a god damn mini map.

• Also I haven't figured out if there is a telltale way to know which fast travel station is close to a mission. Like there is no clue if an area I haven't discovered branches off Rust Commons East or RC West. Lots of wasted time.

• Playing with friends, I find that guns and relics are hardly ever traded, just given.  So I would like friends list mailboxes to drop things in to, whether the dude is online with me or not.  "Here's all this Ranger shit, enjoy."  This could be expanded to allow you to mail yourself stuff for your other characters. 

• I won't ask for a better story, because when playing and Skyping with friends, I don't read a damn thing.  I'm happy with the cutscenes and voiceovers as-is.

@zudthespud said:

" All I want from a Borderlands sequel is that it is called Morederlands. "

That's a pretty solid list.  I'd add integration of Knoxx's vehicles into other maps, as well as more quests in the second large hub area in the flatlands.

I'd like the bullets to be faster and for enemies to not instantly react to your first shot when they don't know you're there yet.  These two things make sniping at range stupidly hard at times.  You line up a shot on a stationary target, you shoot, he (and all his buddies) suddenly jump to the side and start firing back causing your bullet to miss completely.  It affects other guns too, but to a lesser extent.
 
@marioncobretti:
There's an option to turn off duels.  I think it's in the gameplay menu.  As long as you have it off, they can melee you all they want and nothing will happen.  It also means you can't initiate one either.

" I'd like the bullets to be faster and for enemies to not instantly react to your first shot when they don't know you're there yet.  These two things make sniping at range stupidly hard at times.  You line up a shot on a stationary target, you shoot, he (and all his buddies) suddenly jump to the side and start firing back causing your bullet to miss completely.  It affects other guns too, but to a lesser extent.
 

For fucks sake give me a goddamn mini-map!!!!  The lack thereof is the single most infuriating thing about this game for me.

" Yeah, when ever I ask anyone to help me with that DLC, they just laugh.  *An actual story *More Classes *Weapon Trading/Crafting *Keep the Comedy *Make the action skills/Class Mods more specialized  Otherwise, One of my favorite RPG Shooters of all time. "

Good points.  I agree with most of it.  I don't need crafting though... I do enough management of my inventory as it is, so I don't want to have more of that. 
 
Rocket launchers are great if you find ones that shoot 3 rockets at once.  Because there's surprisingly little splash damage for rockets in Borderlands, the extra rockets account for this.  I played through a lot of the Crimson Lance areas of the game with a 3x fire triple rocket launcher and just burned every enemy to death with minimal aiming required. 
 
I think the lack of fast-travel for DLC must be a technical limitation.  It's just too bad that instead of designing the DLC around that problem, they just decided it was okay to let you waste 10 minutes travelling every time you load DLC up for a play session.

more customizable characters would be greatly loved!

I don't mind the lack of minimap, but it could prolly be useful for future iteration so go ahead. 
I guess I'm one of the few people who love The Underdome. Me and my friend grind it all the time and we always have a blast doing so. Any gripe I might have with it is weighed up by the glorious music and Moxxi herself. Her comments are always a treat. Now Zombie Island I could never fully get into though. Luckily it's short!
  
- The level designers did a superb job with the world, I swear - everywhere I turn I could take a screenshot and send a postcard to my mom, however! Some more varied environments couldn't hurt for the next one. Salt Flats was introduced too late into the game and the whole ascension setpiece at the end with the snow could be really interesting if they built some more around that.
- Rocket launchers are a problem, as is alot of multiplayer bugs. 
- Crafting would render the bazillion amounts of guns completely useless so to add this would be insane (though to be honest I admit I've wished I could alter the weapon specs at times) 
- The writing and voice talents of this game are of AAA quality (seriously), so I wouldn't mind more of that, but not to the point where every 20 minutes would be punctuated with a cutscene of sorts. 
- Trading, yes. 
- Character customization to some extent, but keep the four characters from the first one. I think choosing between a couple of different skins would be best. It's important not to lost the essance of the characters.. of the characters. 
- I don't want super advanced artificial intelligens but I wouldn't mind some better, thank you. 
- And finally -- MOAR SKAGS.

1 thing i would LOVE would be drops of both guns AND add ons. like dropping scopes etc. i've had some pretty good guns that i hated to use cause of their scopes.

Frame rate issues. Playing on the 360, I've had a few near impossible boss battles because the frame rate drops to nothing. And then, while the game is playing in single player, enemies will begin to lag around the area. Lag? Really? For Underdome, checkpoint after every wave. I don't even want the cheapness of the two similar events from the main game where you can run back in if the last enemy killed you and he is all that is left. But when I get killed because my character got stuck inside of an invisible wall on the boss wave of round five, and I am back to starter wave of round 4 I want to break the game. And for Knoxx, ninja assassins should not be able to kick me from one catwalk area, over the road, over the catwalk area on the other side of the road, and to my death. And Knoxx is way too large for there to not be fast travel in it. Especially when to get to one area I have to get out of my car, fight a bunch of enemies, spawn a new car (don't accidentally teleport or you get to do it all again, and then continue driving. I understand they want us to drive and use the new vehicles. But I'm not even using a vehicle for half of that. Oh, and last, vehicles should not be allowed to be stuck on rocks. And if they are stuck on rocks, there should be a way to rock them off. And if I can't rock it off, and jump out of the vehicle, I should not immediately get stuck behind the rock the vehicle is stuck on, unable to escape.

I want more enemy variety, more weapon variety, and more classes to choose from.
 
Also, I S-ranked Borderlands, until Mad Moxxi, after that hell-hole I stopped buying Borderlands DLC.

" @Ronald/: What you said about lag reminded me. All the particle effects are really badly optimized. Smoke, blood, acid - you name it. They do awful things to the game. "

I want the characters to have some actual character. In fact, give me a clean slate, one character to customize to my hearts wish, let me pick the type they are (In style with Mass Effect) and give it some goddamn story.

Trade system, including a system with which to transfer items between characters. 
Not a fucking Snake Loot system. Either Round Robin or loot rolls or certain classes get priority on certain weapons or something.
 
How about a goddamn better map system, including a minimap.
 
How about a better PC port? Jesus Christ, every menu is clunky as shit.
 
@Damien said:

" -FIx the online coop in general, so after I leave a random game, my quest log isn't full of quests I haven't started yet.  Somehow the questing during online needs to be fixed. "

Some randomized areas. After spending nearly 70 hours with the game I can get through that first section and find every little hidden thing without so much as batting and eye.

" All I want from a Borderlands sequel is that it is called Morederlands. "

How about a Torchlight style companion that you can give stuff to go sell back for you, and can help fight mobs. Shit, make it a ClapTrap we can customize!

I can't think of anything new, but I'll add my agreement to what other people have said.  
 
1) Fast travel in DLC 
2) Mini-map 
3) Companion (maybe a claptrap) for loot, etc. 
4) Weapon customization - I'm not saying a full fledged crafting system is necessary, but  add-on or upgrade drops (for mags, scopes, etc) would be nice. Also, a general purpose weapon upgrade kit. Example, if I have a level 40 gun I like, it would be cool to find an one-use upgrade kit that increases the gun to level 45 and improves the stats accordingly (Personally, I'm level 61 and still use a level 31 double anarachy SMG with nice extras - I'd love to upgrade that bad boy).   
 
In broader terms (Borderlands 2), my  suggestions would be: 
1) More story. Doesn't have to be a novel. Just something to add a little more personality to the game. Is it kinda sad when the best character in the game is a dancing robot? 
2) More NPCs. I don't want to talk to them or anything, but it would be nice if T-Bone Junction actually felt alive. Have people walking around, getting drinks, driving some cars (getting drinks then driving cars). 
3) Customizable characters. I want to make my own character. Both how they look and what type of "class" they are.  
4) Armor. 

I cant see their damn legs! Borderlands should include legs

" Is it kinda sad when the best character in the game is a dancing robot?  "