I still play TFC. I love the game, and probably won't put it down until the day I die. I would LOVE to see some "escape" maps, such as "thegame", "k_thegame", etc... I would also love to see some other maps ported over(55, bounce, nuclear, and many many more) to FF.
Half Life, TFC, and some of the other old-school mods will never stop being fun. They Hunger is another favorite of mine, although I can't get it to work on Steam.
But this is why I keep older systems around the house.