Honestly, it depends on where you live.
Secondly, I think Impulse is a better platform for digital distribution.
However, Steam's launchpad system to talk to people while in a game is pretty cool for people who didn't realize Xfire's done it for years, I guess.
People like me don't generally like to be always available to everyone on my list, so I just don't add half my games to my Steam profile (Believe me, I don't need my 'friends' telling me to go tank hard-mode progression when I'm playing SupCom. :/)
All of this said, it's still great. The deals are great, the multiplayer community it creates is great, the prices where I live are good, and it's a good way to stay in contact with people from multiple games or real life (Offtopic, girls give out their steam ID more than their phone number I realized, just try it one day.)
Considering that Steam -itself- is FREE, I don't think it can possibly be overpriced.