Most RPG's are incredibly repetitive. Town, dungeon, random encounter, three steps, another random encounter, three steps, boss/hidden treasure (or boss AND hidden treasure), back to town, repeat. However, seeing the story advance is a big incentive - big enough to keep players playing.
Extreme repetitivity is also acceptable in well-designed puzzle games. There was a time when I could spend more time at once playing Puzzle Bobble than any other game.