Haha, I love the puppet idea. That would be fun to see.
My game with be one massive city. Of course, portions of it won't be acessible without certain characters, etc. It would sort of be like Resident Evil, but without wasting time on going through doors, you would pass through them like Eternal Darkness. My game would also have a lot of depth in it too. For example, a character would be able to pick a rod that was broken down that could be used as a weapon. He could stab zombies with it, even throw it, and pick it out of enemies too. I also want to add a system where you can swap charavcters at the press of a button, sort of like pressing Z to select one for quick access. Or pausing and choosing from a screen. I'd also like to setup a strategy system for killing enemies. For example, while you are playing with Character #1, you could order the other characters not to use guns on the enemies, but characters with knives, rods, etc. could attack. So while you are playing, computer AI won't waste up your bullets. Another option could be, is if you are getting too injured the gun-holding chars can shoot down an enemy without having to be ordered to do so. I would do a system along the lines of that, so you can control everything. I have soo many ideas form my head...its just a mess of thoughts, hehe.
I've always wanted a fighting game with more control over blocking, swiping, etc. too. It would be difficult to master, but a real great way to show off your skills.