Impossible to say, because when most of those genres are done RIGHT, I could enjoy a game from any one of them. Generally.
But if I had to choose... cRPG, action RPG, strategy games (Starcraft, Age of Empires, Civilization), and FPS (Half-Life, any game that goes beyond pew pew grafixlawls, and the classics... you can't mess with the classics like Doom).
Was introduced to the Fallout games only recently (relatively... maybe 2 or 3 years ago, I finally decided it was time to see what the fuss was about). What a lasting impression those two - yes, TWO, not THREE - games have left.
Age of Empires is a TERRIFIC series. Starcraft and C&C may hold a dominion over it, but Microsoft's game really is one that stands out as really interesting and entertaining. Just doesn't seem to have the longevity as the rest.
