Steam I have. TF2 I own but don't play - just not my thing. I'm much more a fan of L4D and its sequel. Despite having it in the name, Team Fortress 2 most often feels very much less like a "team" game than a fragfest, whereas in Left 4 Dead teamwork is the core of gameplay.
That and I'm just worlds better at L4D than TF2. >.>;
First, TF2 plays very differently from most FPS games, so the difficulty in translating L4D skill into it is understandable.
In regard to the teamwork issue, yeah, if you play on random servers, it tends to come together very infrequently. The game is rather balanced for team synergy, though. I've got over 1000 hours of playtime (yay college!), and I've learned the strengths and weaknesses of each class pretty intimately. If you spend a bit of time finding some good servers and stick with a class or two to be your foundation, the game gets really fun.
If anyone's got questions, I can offer my knowledge (and ability to wiki-search).