Left 4 Dead. I played the RE5 demo and hated it. Mostly for the controls. Look at this:
http://majornelson.com/ Left 4 Dead has been in the top 10 since it came out because of it's awesome replay value. RE5 is up there just this week, but #5 isn't a very promising starting position for a game with no mutiplayer. I'm just talking replayability here....
I found Left 4 Dead more entertaining overall. It's great, but even better if you have friends who have the game too.