So I have had Left 4 Dead for my XBOX 360 since it came out but I really didn't get into it. I decided to get it on Steam and have been playing it a lot more. I really didn't realize how much I missed the keyboard + mouse combination for first person shooters. I was actually pretty good at the game. I got a nice headset and started playing online. All the folks I have played with so far have been great! (which was the exact opposite online)
The whole Steam setup is really nice. I like all the integrated tools - makes it almost like XBOX Live. Newer games, like Left 4 Dead, also have achievements.