For those of you who enjoy zombie horror, Valve's FPS Left 4 Dead is worth checking out. Basically, you control one of four survivors trying to make it out of a zombie ridden area. In addition to 28 Days Later style "infected", there are "special infected"- mutant zombies with unusual abilities such as the pouncing Hunter and the zombie attracting bile spewing Boomer. It uses the Source engine, so nothing revolutionary, but adds some cool cinematic effects like film graining and color scaling (IE most colors look a bit washed out but red is quite bright) that do a good job of capturing the mood. The sound is very well done, and has a dynamically generated score that reflects what is going on in the game. So if you hear the music ramp up to a crescendo, for example, you know the Horde (a huge mass of zombies) is coming. And each zombie emits appropriate groans, snarls, gurgles and screams. Which can be quite disconcerting when you hear them before seeing them! The game also has an interesting scaling difficulty system based on the AI director. Essentially the director monitors character stress levels and adjusts enemy rations, item placement, etc. to fit the selected difficulty. So if you are getting savagely beaten on Easy, it will cut it back. But if you are cruising through Expert, it's going to ramp it up until you don't feel like such a tough guy.
Multiplayer offers two modes. Cooperative, where each person controls a survivor (AI controls any extras), and Versus, where players are assigned to the Survivors or Infected. Infected try to stop Survivors from making it to the Safe Room. Cooperative with friends is much more fun than using the AI, as you can coordinate much more effectively and actually employ something resembling tactics. Versus is a heck of alot of fun, but I found that I greatly prefer playing as Infected for the different playstyle (though a good Survivor team is hard to stop- given equal skill, Survivors should finish the round). Since the Survivors do seem to be much stronger, it is extremely satisfying to finish them off!
All around, a very fun game and has actually distracted me a bit from my reigning favorite, Company of Heroes. At least until Tales of Valor is released.