"TF2 = HL2 multiplayer. Free download. I called it 16 months ago, I'm sticking to it now."
Cept Valve keeps saying that it's not HL2 MP, and that TF2 will be a standalone product on the Source engine. It wouldn't fit as HL2's MP anyway, because whatever it is, it's supposed to be HL universe themed (i.e. Gordon and pals), and TF2 is not.