In terms of DLC I'd like:
Vehicle: Mako
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Seriously, I loved that thing. It was great fun bumping around planet surfaces, exploring the landscape, prance about with the shifty-looking cow and the space monkeys... The Hammerhead I found rather pale by comparison. So something like the Firewalker pack in ME2, only with the Mako.
Lost War Assets
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Story-based DLC that ties into the main story and lets Shepard recruit other races like the Volus, Elcor, Drell and Hanar. Probably something about Project Phoenix, now that their Biotics made it into multiplayer.
The Resistance
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A side story that puts you in Anderson's or Coats' shoes during the time Shepard drums up support throughout the galaxy.
Blasto
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Probably great for an April 4th release, they could make a playable feature-length Blasto movie as DLC. I'd totally buy that.
But, much more importantly, where do we go from here?
Well, obviously, Bioware should do what Bioware does best: Another Mass Effect RPG like this one! Apart from that...
- A third person stealth game in the vein of Splinter Cell: Chaos Theory. With a Salarian main character. We've heard about the Silent Step and the Ever Alert before, but now I wanna play them. Preferrably with character customisation and a Bioware-ish dialogue thingy for additional interactivity.
- An old-school space flight sim like Star Wars: TIE Fighter. Like they used to make them: Awesome fully-rendered cinematics, controls that utilize the whole keyboard... Granted, the genre seems to be more than dead, but if anything could revive it...
- A game where you play a powerful biotic. Something that'd play like Prototype in terms of free-roaming and stuff. With Jack as the protagonist
Things I don't want to see:
- Real time strategy: While I used to be a fan, I've grown tired of these, so I'd rather see the ressources going elsewhere. I like my Mass Effect stories more personal, too.
- MMO: There's too many of those anyway. Also, I can't play an additional MMO.