Hahah, I didn't even know it was available for the home computer.
Several years ago, I was living with my brother, who was (and maybe still is) a L4D2 addict. He played it on the XBox. He played EVERY night of the year, for many years straight, with a crew that was very serious about it. I must have watched him play 1000 times or more. I had most of the levels memorized.
I bet you're really good! What character do you like to play, and what are your favourite special infected?