having recently watched Dead Set and replayed Resi Evil 1 on the Cube, my mate and I were discussing the ultimate zombie game. Basically it would be like a cross between Fallout 3 (with different factions to associate yourself with, and rpg elements involving combat and leadership of people) Dead Rising (with the idea that everything is a weapon, and that you can lead survivors to a safe house) 28 Days Later (in that they wouldn't be zombies, but the fast running infected, and a lot of the time, your best option is to just run away- making it more survival based than combat, unless there is only one, in which case the combat could be similar to Condemned 2) GTA IV (in that you can borrow any vehicle, and attempt to use weapons you find, and also controls and feel of the game as you play would be very similar to this) and San Andreas (you start off in a rural environment, like that bit that was in the bottom left corner near the mountain). However, the main emphasis of the game would be survival, so you have to find food for yourself and the rest of your fellows who you may have saved. All people would have a purpose, like if you rescue a soldier, he'll use combat to keep people away from you. Save a doctor, he'll heal any wounds you might get. Or you can say screw you to them and run for it. In this way, the squad element would be kind of Bioware-ish (think Mass Effect or KOTOR). The story would have to require you to keep moving around, so that you go from small village to medium town to full scale war and sheltering in a city.
I'd call it "28 Condemned Days after the Rising Fallout: Mass Theft Andreas Republic"