Future Perfect has a fun campaign, and it and TS2 have "Arcade" mode which is a collection of custom scenarios/objectives set in multiplayer maps with high scores and medals and shit like that. It's fairly standard FPS fare at its core, but like, in a good way, and there's tons of varied stuff to do. Good sense of humor, pokes fun at time travel weirdness, lots of nods to classic movies/games and their tropes.

I will say that their real staying power came from couch multiplayer and the mapmaker, which I don't imagine will matter all that much on an emulator.