I've played TF2 only once or twice myself, but I still recognized it as being a fantastic game; besides, Portal and the HL2 series more than carried their weight. (Hell, I think I would have payed $50 for Portal itself.) The only game I've traditionally played online is Descent 3, but I'm willing to try out a good thing when I recognize it.
Speaking of, we really need to try organizing another HLP TF2 gameday. We have that Steam group going, so we might as well use it. The reason I haven't broken into TF2 is because I don't know what I'm doing with it (I really wish Valve had included some sort of singleplayer training/tutorial mode), but I'd love to change that.