Steam = No buy.
For everything everyone already said (and for half dozen hours lost on Steam troubles for the measly 3 games i have there)) and for the fact that it forces you to have all your Steam stuff in a single physical location (or ridiculous use of symlinks).
Results could go in the 1st post, no? It made 28th on eurogamer (http://www.eurogamer.net/articles/2010-12-23-eurogamer-readers-top-50-games-of-2010-50-11-article?page=2)
(loved that it came in front of pacman).