Get it. It's not just your standard FPS. It's Half-Life. It's something a hell of a lot better than the original. That, and TF2 is a shitload of fun.
Most importantly, play Portal. It's worth every cent of that price just to play that. You're not going to expect much, but in return, you'll get a lot out of it. It's the most interesting game I've played this year. An FPS that doesn't involve shooting, really.