This is pretty much an unknown mod for UT2K3; it's kinda short (and old) but well worth the download for those who are Zombie fans (yeah, you need to have UT2K3 installed):
Infection places you as a man in a small town that's infested with mutated zombies and monsters. This single-player horror themed total conversion has the feel of the popular "They Hunger" for Half-Life with the beautiful Unreal Tournament 2003 engine..
Download: