Most shooters seem highly repetitive to me. I might play one every now and again, but I watch my wife or son spend hundreds of hours on them, and I am astounded how they can do it. Choose beween 6-15 different weapons, kill one guy, use cover to hide from another, die, respawn, wash rinse repeat.
(bonus points goes to Transformers: War for cybertron's campaign mode for it taking repetition to a whole new level)
Rhythm games, but you couldnt have a game like that exist without repetition.
Most final fantasy games. If youve seen one recolored slime NPC youve seen them all.