I remember trying to start something like this off way back when, so let's at least start with proposals for the game. This being Bay12, if it's going to be made by the community, then it'll have to be playable by the community ie, if you can run Dwarf Fortress, then you should be able to run this game. So lets get the details in an easy to read way down:
-Multiplatform: playable on macs, PCs, and Linux. We'll prolly have to use Opengl for this.
-Low on the graphical end (Though I'll be suprised if we hit that)
-Free
Anyway, it might be best to vote up a genre next, now that we have ground rules, so here we go:
-platformer
-RPG
-Puzzel
-Shmup
This is all I can think of off the top of my head, so others will prolly be able to suggest more.
And before we're done, we'll also need to figure out a general idea of how the game ought to be conducted, and the kinds of emotion we want to evoke in the player, aswell as a general playstyle.
As for something I'd like to see,
Genre: Platformer, with RPG elements
I really liked spelunky, but after a while it felt same old same old. Being able to expand on that game, and add more complexity might be fun, at the expense of slowing the action down a smidge to encourage more thinking and less reacting.
In the meantime, I can see if I can make simple graphics for Hitpoints and Defence, since we'll prolly need them no matter what the game we're making is going to be.