Thank you, Cracked, for making me think of this way too much. Mine would be an open world robot fighting game. Basically the Burnout series, but robots instead of cars. You could be a robot with the capacity to upgrade yourself, or just someone who has a remote-control, either works. First would be cooler though. Imagine trying to hide the fact that you're a robot from unsuspecting civilians. That'd probably involve hooded cloaks and stuff earlier on, and you'd have the option to look more and more human and blend in like a normal person while running around fighting/causing crime at night, sticking to the 'constantly disguised very well' thing, or just saying fuck it and being a robot supervillain. Or superhero, though that might be harder.
You'd be able to upgrade yourself and get weaponry and so on, and when you accrued damage you'd have to repair yourself (because robots don't heal naturally--although there would probably be some sort of auto-repair system you could build/get). And there'd be quests of course, and consequences to how NPCs react to you based on whether or not you blow your cover. Ideally it'd be a large city and you could relocate to another district or something if people started to get suspicious of you. Or you could intentionally blow your cover and let the world react to a robot superhero/villain.
Some point into the game, there'd start being other robots that could think and upgrade themselves. (Until then there'd just be drones, remote control or with very limited AI.) If you beat them but don't destroy them, then they upgrade and come after you again. Or you could take their quests and have them give you things and otherwise leave you alone. Maybe there'd be the odd helpful human NPC, but the focus should be on the robots.
Buy stuff or steal stuff? Smash things or protect things from the other ones? Defensive mode (energy shields, super armor, etc) or all the weapons? Do you want to be able to jump really high or fly, or do you want to blend in as much as possible and be limited to relatively human climbing--or do you want to forgo subtlety entirely and just scale buildings in full daylight? Do you want to build your own robot drones as scouts, or even do combat with them only, avoiding upgrading yourself and acting as basically the remote control, or are you going to go it alone?
Essentially aspects would be the upgrading, unlocking new areas and new parts, comboing the parts in different ways, a gradual time scale that includes day and night, and NPC reactions. Hell, essential aspects. That's pretty much the whole game.
So basically: screw plots and character development, I want a game where I can play as a robot fighting other robots and capable of doing anything with all the things.
...God, that sounds like 'The Life of Proto Man: The Video Game' now, doesn't it? Fuck it, I'd play it even if it weren't a Mega Man game.