I think if you are looking for a good game to play with your friends, be able to go all Coop, this is the game for you.

User Rating: 9 | Left 4 Dead X360
This game gives nothing more that it was made for, it is by far a great multiplayer and creates dramatic atmosphere with music and sounds. Sure, it isn't that long, but some downloadable content will eventually come. They have already released more multiplayer maps, but I think that people are waiting for other playing modes like horde or even survival. Put each person in a house and see who can withstand and out battle the zombie waves. So this could be both a multi player and a single player game mode. (more guns and maps are always good too)

Best part is, and what I recommend to everyone, after playing it with friends, try it on Expert. You will find a true challenge, sometimes even unreal and the achievements, although hard, are really rewarding. You don't have to go out of your way to get all of them, you just have to play the game and get to try it in different ways.
I even think that it's missing achievements for the guns, and how many kills you get with them.

I hope that everyone that buys this enjoys it, always fun to play, hope more things come for it in the future.