Left 4 Dead is, in my opinion, the best zombie game so far. People may say there is not enough content, but i can assure you that if you buy it, you will be playing it for a while, and once in a while you will always go back to it. It's just that replayable. There are 4 campaigns, but again, they are highly replayable. The campaigns are fun to play alone, but is extremely fun to play with friends. If you want a challenge, all you have to do is put this game on expert. Beating the campaigns on expert level is damn near impossible playing single player, but if you are playing with friends, expect a huge challenge and loads of fun. There is also a versus mode in which you play as teh survivors as well as the zombies! Finally a game where you can play as a zombie! This game is really great and I would recommend it to the most hardcore player and someone who doesn't even play games at all. You have to love Valve.
