Left 4 Dead 2

One of the best multiplayer games for the PC ever.

I loved L4D1, and L4D2 just expands on a great game
More weapons, more zombie variety, more gametypes, more gore, better graphics, improved AI director, and probably more things that I am missing.
Get some friends together for a game, and try to not have a great time.

Perfect score. Left for Dead 1 was a great game, and the second installment makes absolutely everything even better. The graphics, in less than a year between games, have improved significantly with way more detailed environments and enemies, with the gore level shooting through the roof. Every zombie here seems to have a full skeleton and organ system, which you will see in abundance. The banter between the characters is just as funny as the first game, if not moreso. The weapon selection has also expanded brilliantly with the addition of several new guns and a boatload of melee weapons, which are crazy fun to use (instead of being the gimmick I thought they would be). So seriously, if you missed the first one then get this. If you liked the first one, get this. If you like zombies, get this. Or if you like shooters in general, get this.