A very fun Mario RPG
Finally, it has a different story then just killing Bowser and saving Princess Peach. You get to roam around the Beanbean Kingdom freely, killing any enemies in sight. There is different stuff to wear and equip, boosting your stats. Lots of places to explore. Memorable music. The graphics are good for the GBA. There are some side quests in the game too. A Plot-Twisting turn makes you really pissed (well, at least it made me feel pissed).
The only problem with this game is the difficulty -- it's too easy. If you just repeatedly use your bonus stats for leveling up on Power, you will have NO PROBLEM killling bosses. Even the final boss in this game will probably only take you about 2 tries with Bros. Attacks.
Hands off to Mario and Luigi: Superstar Saga, one of the best GBA games ever!