I play shooter games alot
Bioshock series (shooter/fantasy/horror)
Fallout series (shooter/rpg/post-apocalyptic world/steampunk)
Borderlands Series (shooter/rpg/steampunk)
Farcry 3 (shooter/rpg/island-jungle environment)
Dead Space series(Space/survival-horror)
Oblivion and Skyrim (Adventure/fantasy)
They are all very well reviewed games, dead space and bioshock might be less replayable though because it is no quite open world, but the other games feature very vast worlds that make the experience replayable and don't feel like it's the same game when you give it a second (or third) spin.