Steam works well if you have a constant broad band connection. It is nice for keeping the Valve games organized and updated; and it really helps with finding servers. However, if you are one of many who do not have a constant internet connection (or none at all) then you're out of luck, Valve gives you the finger and you're out $50 (until you return it).
This was my case with HL2, I installed it, was so excited, got all my hopes up, clicked on the icon and got nothing but Steam's account and game verification crap. What's worse, is that because I have no connection in my room, I had to rip out my rig and reconnect everything where I could get a connection, but as if that wasn't enough, after I thought I had finally appeased the Steam gods, I took it back up to my room, tried to play, and the f***ing thing still wouldn't work! AAAAAAAAAHHHHHHHHH!
Anyway, I think Steam is a great idea, but very poorly executed, you shouldn't need to have an internet connection to play single player games. (Yes, I know about the off-line mode, but it's been my experience that getting it to work is a craps shoot at best).