I know I’m late to the party on discussing this but what changes would you like to see in Borderlands 2. For me this is what I would want.

1. A weapons trading system. We all had awesome weapons that we had no intention of using. It would be great to trade with other players.

2. Ability to customize weapons. At the end of the day there were some weapons that I grew so attached to that I felt bad when I had to let it go. Or even more frequently, there were weapons that were one part away from being useful to me. I would have loved the ability to tweak some of weapons.

3. More diverse environments? It really didn’t bother me while I was playing the game but it would be nice. Pandora isn’t a wasteland so in theory there should be some different environments to see.

4. Better story. The story in Borderlands was actually interesting. I would daresay it had the potential to be great. However it didn’t quite mesh at the end of the day. The DLC, with the exception of Mad Moxxi, did a much better job of telling a story so if they continue from there I have no doubt it could be even better.

5. Ability to turn on and off online play without quitting out. I preferred playing the game as a single-player experience but occasionally I didn’t mind if some randoms came into my game. However to allow that you had to quit out and turn that feature on. Just put that in the pause menu Gearbox.

6. Better Rocket Launchers. In a game that had such fun shooting I was shocked to realize that the rocket launchers were all but useless. I barely used them.

7. No level cap.

Anyway, despite these requested changes I still love that game a ton. In fact if they gave me the same game with new environments I would be happy to pay $60. I just hope I can still play the game single-player and that they have another Roland in the game. Something tells me though they’ll try to “balance” the characters more.

Better driving. And an ending boss that doesn't suck. 
 
Also it's kind of a weird request, but I don't want the original four characters to return as the playable cast in the sequel. Naturally because they're all uber-experienced by this point, if the game is continuing the canon and characters the original, and it'd be pretty cool to have them as friendly NPC's who could potentially train, give quests and fight alongside in Borderlands 2. Would actually allow them to flesh out their personalities a little, and it'd be neat for them to possibly make some more of that trademark fourth wall humour and comment on stuff from Borderlands.

No level cap? What games have no level caps?

No Gamespy, a proper UI for PC and split screen co-op that doesn't seem like it was a last minute thought, in Borderlands the UI's didn't even fit properly.

I really want this game to take place in a completetley different enviorment. The wastelandy badlands were nice at first but man did it lose it's charm and just become boring after the 10th hour.
 
More space related yet. Yo your universe has spaceships use them.
 
More customization.
 
It would also be cool if they increased the amount of players in one game. It always sucked when a fifth person got on and you were already full.

More character classes, maybe the ability to import a character from borderlands into this one. Either a higher level cap, or no level cap at all. And a bank to store items and weapons, I also like the idea of the weapons trading system you mentioned.

Fun character skills.
 
I  thought they were all very boring. All the classes seemed too similar to me.
 
I understand they weren't going for a hardcore RPG audience or anything, but more customization would be nice.

Slightly better AI? 

Grenade Launchers that can use the grenade mods anyone? Also would like the rocket launchers to do damage against bosses. They are actually good when you find X4 elemental one, but only against normal units. The only problem is when me and my friend got to a boss that could only be killed by critical shots, I had to sit there with my thumb up my ass. Bricks special ability also needs to be changed! It was useless after level 10. Or just give the new rocket / grenademan a good ability if Brick isn't in it.

Better driving. And an ending boss that doesn't suck.  Also it's kind of a weird request, but I don't want the original four characters to return as the playable cast in the sequel. Naturally because they're all uber-experienced by this point, if the game is continuing the canon and characters the original, and it'd be pretty cool to have them as friendly NPC's who could potentially train, give quests and fight alongside in Borderlands 2. Would actually allow them to flesh out their personalities a little, and it'd be neat for them to possibly make some more of that trademark fourth wall humour and comment on stuff from Borderlands.

The reason I stopped playing Borderlands was because I went too long without getting an awesome weapon drop.  Enemies became bullet-spongy and the game started to become a chore.  Don't know how they could fix that without ruining what was cool about random loot in Borderlands.

Borderlands to me is like a classic , and I believe that they'll make the borderlands 2  way better than the first one....let's wait to play...

Grass, psychos, better loot, better classes, better story.