The recent Bombcast bought this up so I figured I'd make a thread. 
 
The one thing that immediately came to my mind is a game featuring Samara.  I'd like to see her in a less over the top version of a game like Bayonetta.  In her intro movie she was throwing people through walls, throat stomping baddies and (assumption) blowing up someone's head with a biotic blast.  All of that stuff would be pretty fun in an action game.  Plus she can do that biotic powered landing that allows her to jump from high places and float down.  All of that would make for interesting combat in an action game.  Combine that with the solid story telling of Bio-Ware and it'd be a pretty interesting game.  At worst, it'd be a nice test for how, in my dreams at least, a sequel to Jade Empire would play.
 
What's your ideal spin-off?

I stil think Sim Citidel would be a great game XD. There is rampant crime in one of the decks. Add a C-Sec station for 5000 credits, adds +3 to officers and a radius of 10. 
 
On a more serious note, I think exploring the First Contact War would be a brilliant area for future games, either as a straight up shooter or an RTS.

I would really want to see first contact.

A dating sim. 
 
...What? 
 
But seriously though maybe a stealth game were you play as Thane would be cool.

A MGS type game with Thane.
Some sort of "Science Papa" game with Mordin.
A GTA type game with Garrus.
BIOTICS UNLEASHED with Samara and Jack!

I want a Phoenix Wright style game that takes place on the Citadel (or anywhere else I suppose)

Max Payne-esque sci-fi noir with Garrus in the lead role.

" I stil think Sim Citidel would be a great game XD. There is rampant crime in one of the decks. Add a C-Sec station for 5000 credits, adds +3 to officers and a radius of 10.    On a more serious note, I think exploring the First Contact War would be a brilliant area for future games, either as a straight up shooter or an RTS. "

id love to see the back story wars (Frist contact, Rachni, and Krogan rebellion)
maybe one of them in a RTS style

An RTS resource gathering game implemented on planets instead of having to probe scan them.....  you build a base, build some harvesters, defend them from pirate raiders, get resources and get out and continue the game.

" An RTS resource gathering game implemented on planets instead of having to probe scan them.....  you build a base, build some harvesters, defend them from pirate raiders, get resources and get out and continue the game. "

Stealth action game featuring Garrus/Thane.

How 'bout Nintenvarrens or Leisure Suit Legion?

I feel like the amount of lore created by the series lends itself to a Civilization-style game.
 
Maybe EA should take another crack at Spore and set it in the Mass Effect Universe.

None thank you.

I'm guessing since you put this in the Mass Effect 2 forum page that you mean spin offs connected to the Mass Effect 2 characters or universe.
I mean this could've probably served you better if you'd stuck it in the General discussion forum page.
 
None the less my answer would have to be no.
Each studio that designs a game is hopefully specialised in designing that sort of game so a spin off, unless it's in the same design vein, shouldn't really be made. Because it just wouldn't be a very well made game since they're not working to their strengths as a studio.
 
If the spin offs the same, mechanically, as the game that it spun from then that's a different story.
 
In which case, I would have to saaaaaaay... umm... Maybe a game called: "Dog's special adventures" spun off from Half-life 2 universe.
 
I mean it would be pretty sweet being as agile and strong as he is. And while it would be a bit more comical in tone than the original Half-life games tend to be. It would still be an interesting campaign and retain the classic story elements of the original games. (Gordon Freeman dosn't exactly talk much either.)
 
Besides, Valve knows how to make good games.
 
(Maybe you disagree, maybe it's a terrible idea, and I could see why you'd disgree, but if you saw what sort of game I'm imagining in my head you'd like the idea too.) :-)
 
EDIT: Oh! And on the whole subject of a Mass Effect 2 spin off. Why do we need a whole game focused on the spin off story, when we have DLC that does exactly what you're asking about?
Granted from shepard's point of view. But none the less, this's still a good question.

a spin off that doesnt suck

" I'm guessing since you put this in the Mass Effect 2 forum page that you mean spin offs connected to the Mass Effect 2 characters or universe. I mean this could've probably served you better if you'd stuck it in the General discussion forum page.  None the less my answer would have to be no. Each studio that designs a game is hopefully specialised in designing that sort of game so a spin off, unless it's in the same design vein, shouldn't really be made. Because it just wouldn't be a very well made game since they're not working to their strengths as a studio.  If the spin offs the same, mechanically, as the game that it spun from then that's a different story.  In which case, I would have to saaaaaaay... umm... Maybe a game called: "Dog's special adventures" spun off from Half-life 2 universe.  I mean it would be pretty sweet being as agile and strong as he is. And while it would be a bit more comical in tone than the original Half-life games tend to be. It would still be an interesting campaign and retain the classic story elements of the original games. (Gordon Freeman dosn't exactly talk much either.) Besides, Valve knows how to make good games.  (Maybe you disagree, maybe it's a terrible idea, and I could see why you'd disgree, but if you saw what sort of game I'm imagining in my head you'd like the idea too.) :-)  EDIT: Oh! And on the whole subject of a Mass Effect 2 spin off. Why do we need a whole game focused on the spin off story, when we have DLC that does exactly what you're asking about? Granted from shepard's point of view. But none the less, this's still a good question. "

Like Karaoke Revolution, but you play as Moridin.

Ether an RTS where you get the alliance, council feet, or geth; or an space combat game about Joker in flight school.

Jack Black a la Brutal Legend in a Black Hawk Down-esque war game. Like Jim Carrey attempting a serious role! 
 
(Okay, The Number 23 wasn't that bad.)

RTS using each alien race for factions.

I think it would be interesting to have a spinoff where you play different scenarios of species at the point they become extinct. An good example would be if you could play as a prothean right when the reapers invaded or you could play a quarian when the Geth started revolting, I think it would be an interesting way to flesh out the back-stories of those events. 

Mass Effect football. All Krogan defense FTW! Asari and human cheerleaders. Salarian and Volus referees. Elkor and and Salarian commentary.

I want a Mass Effect space trading and combat sim along the vein of Freelancer.  The universe is set up perfectly for it, with the same silly "I'm out of fuel so I stopped moving!" space mechanics as every prior 'space sim' game, which they can almost justify with the way they handle mass effect drives, and who doesn't want to fly around shooting shit up in a ship like the Normandy?

A dating game with krogan

Jack in a dual-stick shooter.

• An "interactive drama" where your actions shape the events of Elcor Hamlet. 14+ hours of riviting action! Comes with free scratch and sniff stickers.

• A shmup - *pew* *pew* *pew* take THAT you stupid reaper!
• An RPG.
  

Elcor Hamlet.
 
Make it happen.

Urdnot Wrex: Krogan Warfare 
 
or 

Blasto the Hanar Spectre: The Game

I really would like to see a Mass Effect MMO. It's a shame Bioware decided to go with the KOTOR franchise for their MMO, because a Mass Effect MMO would facilitate 3rd person multiplayer action with huge hub worlds and possible tens of playable races, with lots of different class types (vanguard, soldier, infiltrator, adept, etc)