Steam users?

If anyone is a steam user, what do you think of the service?

I only used steam because of CS way back in the day, but it looks incredibly fleshed out now. I wonder if it's worth investing into.

I want a PC worth Steam, Half-life, etc.

My only real reason is that i want Garry's mod :p

I have steam, but never really got the urge to get back into some of the games. I like playing some various mods.

I finally installed it again, it actually remembered that I bought the Half-life collection a few years back..pretty awesome.