I downloaded it once it became free and I have a lot of fun on it. I'm not a real gamer (hell, i play on my laptop's trackpad rather than with a mouse) but the game itself is quite balanced and i enjoy the hell out of it.
I've played it on Xbox 360... Pretty fun. The game on PC is on a whole other level though. Valve really took care of their PC fans who owned it. Don't play it often at all, but it is fun and well balanced. Probably the most balanced shooter of this gen.