Trying out this game. It's a zombie survival game that's still in developmental stage but for sale on Steam.
Originally an America's Army mod they're now developing it as a separate game.
It's still pretty rough but shows some potential.

It is unfair, brutal, invites paranoia and violence.
It can get boring on your own, like the time I spent more than an hour running through the wilderness with nothing in sight only to find I ended up running in a large circle.
It can get frustrating when you finally have some decent gear and lose it to some trigger happy co-survivor.