[old woman memories mode]
I remember registering my CD key of HL1 on Steam and was surprised when they gave me the expansions for free. Cool, because I didn't have them.
I remember buying The Orange Box on Steam. I remember it because Steam gave me a warning because I already had Portal - it was free at some point. Was a bit miffed when TF2 went free to play later on.
And I somehow still haven't played HL2 on Steam, I think? I played it about 1/3 way on Xbox 360. Played the shit out of Portal on 360 though.
It's apparently $50 a month, but based on one recent video from a guy who looked into this, there's apparently a hard sell to "commit" to the program for a year, and if you do commit, it won't let you cancel or refund, because you committed to the program, bro, that's a sacred vow, bro, you can't violate that, bro.