If you're interested in at least what it's like to be Infected, the preview talks in-depth about it starting here: http://www.left4dead411.com/left-4-dead-preview-pg10
Sorry for spamming links...I just think if you're remotely interested in the game, you should definitely read that preview.
LEFT4DEAD411.COM
Bet with disolitude: Left4Dead will have a higher Metacritic rating than Project Origin, 3 months after the second game's release. (hasn't been 3 months but it looks like I won :-p )