There's nothing quite like it. I would say Rogue Legacy's main elements are: cartoon visuals, fantasy setting, randomly generated levels on a per-room basis, light permadeath with progression elements, action platformer. Here's a few I would recommend that I think have some overlap in appeal while being different.
Risk of Rain has a more subdued aesthetic, a sci-fi setting, randomly generated spawns and loot inside somewhat more structured levels, heavier permadeath with progression through adding items to the unlock roulette, action platformer (slower in speed and heavier in weight than Rogue Legacy).
Binding of Isaac has a gross bodily fluid flash animation aesthetic, a macabre gothic setting, randomly generated levels on a per-room basis, heavier permadeath with progression through adding items to the unlock roulette, top-down dungeon crawler in the vein of Zelda
FTL is a cartoony, sci-fi setting, randomly generated event, heavy permadeath with limited progression except class unlocks, space exploration / combat / text adventure combination.
Flotilla is a pastel, sci-fi setting, randomly generated event, heavy permadeath with no progression, short space exploration / combat / text adventure combination.