Played Rifts, D&D 4.0, D&D 3.5, Pathfinder, Star Wars D20, Serenity, and Spycraft.
RIFTS: Expansive multiverse combining a very dangerous world with science fiction and magic. Good for heavily story-based games. I have heard, however, that the Palladium rpg books (of which RIFTS is a part) is...