A game in a MASSIVE random/procedurally genned world where the only goal is to wander, and overcome challenges that the world might throw at you.
I was thinking Steampunk universe, probably with anime-esque graphics.
Every biome that you can go through is genned from two lists.
One is a general theme of the biome, and the other is what it actually is.
Like, Stone Forest, or Holy Canyon, or Snowy Plains, etc.
After the general biome is genned, creatures are genned for the region with a set of parameters.
Size, Predator, Nocturnal, Material, Type, etc.
So while I'm camping out in a Stone Forest at night, I can be attacked by a pack of Lightning Wolves, or something.
Bandits are also a problem in whatever biomes they get selected to be in.
You can build land, and maybe air vehicles, I mean, it is a steampunk game, innit?
The game would have heavily orchestral music, for both combat and general wandering.
When in a vehicle, music is genned based on how fast you are moving, so combat between two fast moving vehicles would have a faster paced music than combat in a slow vehicle.
The game would have a third person perspective when on foot, with the option to switch to a isometric perspective when in a vehicle.
You can hire mercenaries, or even make friends that follow you for free on your journey.
I think I've covered all the bases here.