When I had bought Halflife 2 about  year or so back , the bundle had come along with Counterstrike Source.
Initial pains with the steam platform which Valve uses almost made me uninstall the whole thing ... 5 cd's for insallation and then another 5 hours to update (/decrypt/whatever they call it) ?!
Thankfully , I stuck with it and continued on with HL2.
Never got around to completing HL2 ... the stress on puzzle solving was irritatingly high and pretty soon I got bored and turned my attention to Counterstrike.
I have never looked back since - though the bots typically suck , the online gameplay is pretty awesome !

Considering my connection speeds at home , I am really impressed at the low latency and the gameplay expierence. You do get to meet lot of 'interesting characters' online - including damn good players , people who are pretty passionate about the game and the normal bunch of cheating losers , so-so players like me , and n00bs ... it is nice fun all in all !
So now , when I am not doing anything interesting , I am on CSS