Knyte wrote:

There is a HL2 mod that is a zombie vs human game. The human have to fight for what few weapons and armor their is, while the zombies have thier claws and teeth and don't need to worry about weapons. It's kinda fun, but you don't really get the "overrun by zombies" feeling when it's 10 zombies vs 10 humans.

That is Zombie Panic. But you are right, it doesn't have that overwhelming feel but I still like it.
Though recently I did find a Zombie Mod server in CS:S that does give you that feeling. You have to kill a certain amount of zombies and in the end if you die twice you become one. The maps on that server give it the feeling of a zombie takeover.