I actually got this this friday and played through it this weekend. Amazing game and I was probably the only person on earth that hadn't played it up to this point. My god the ending credits song is epic! Just blazed through the advanced missions and getting rocked in speed runs.
On another note I used to be pretty anti-steam, mostly because of a good buddy of mine who had a fair share of bad experiences with it (a while ago though), so I was really hesitant. But I really wanted to get into team fortress 2 so I went for it and have been very happy with it. I'm not going to call it the best delivery platform out there but its certainly not horrible /shrug.