This was the best game purchase I've made in a long time. Hadn't gotten either of the HL episodes, and enjoyed both 1 and 2, though Valve needs to speed up their release tming if they plan to continue episodic content for the series.
Never played the original TF, but have been having a blast with TF2, there are a fair number of servers running custom maps, and that has definitely added to the fun. After 2+ years of Battlefield 2 being my primary FPS for online play, I'm happy to finally ditch it for Team Fortress 2.
Portal was really the gem of the package though. The writing was some of the best ever in a game, and took a great concept and turned into "Game of the Year" quality. I definitely need more maps. I've played through it completely twice (once with the commentary option), beaten the advanced maps, and am now working on the challenge maps. The fewest portals challenge was a lot of fun. You can beat half of them with only 2 portals. The fewest steps and least time challenges are giving me much more trouble. I am still resisting the urge to look at walkthroughs. but only barely.
If you are into FPS games even a little, you really can't find a much better buy than the orange box.