Mario and Luigi: Superstar Saga is a Nintendo RPG on the Game Boy Advance, starring characters from the Mario universe.
This game is a bit of a departure from a traditional RPG formula. This game continues the tradition of more casual RPGs, first established by Mario RPG. There are only two party members, Mario and Luigi, and each has an action button dedicated to them, both in and out of battle. In my opinion, the game plays more like a platformer, and it includes puzzles based around the brothers' team abilities. This adds a puzzle element that I appreciated as a break from battling.
The game also follows the Mario RPS tradition of never taking itself very seriously. The game is set in the neighboring Beanbean Kingdom, and is infused with a host of bizarre characters and slapstick humor. I think that this game is one of the better RPGs on the GBA, and is notable for its humor and unique battle system.