If you want massively-multi-player survival horror, you can't go passed Day Z. The Alpha of DayZ is finally here on Steam Early Access, and the trailer is pretty full-on.
Most games would artfully pull away from someone shooting themselves in the head, but not Day Z. Day Z wants you to see brains on a tree as zombies swarm in for a delicious human meal.
Honestly, I just want to go home and play this right-freaking now.