I don't like Steam at all really, I put up with it for HL2 but out of choice I wouldn't bother.
a) It's forced, and for some people, unnecessary. I just want to play HL2. Why must I install some utility that I won't use most of the features of, then update it, and update the game, etc. etc. etc.
b) And what would happen if Valve were ever to come into any kind of financial difficulty? Could the games purchased be guaranteed to work afterwards?
c) Placing the control of my account in the hands of a company isn't something that appeals either. They have the ability to just cut me off as and when they see fit, whether i've broken any rules or not. I appreciate that it's rare to just get VAC banned for no reason, but there is a chance of it happening. And then it's got to be chased up and sorted.
For the same reasons I don't want Games for Windows Live either.