The very, very, best RPG out there ever on the GBA!!! Period.
The gameplay is the standard RPG formula:you hit him, he hits you, and you heal another party member with a herb or a potion. Duh. You can have up to 4 in your fighting party, and you can switch fighting party members once you've acquired enough. There's also something like Final Fantasy's job system, but you don't unlock them, instead you change your job by kind of equiping these magical creatures called Djinn. Not only do they change your "job", they also make you character more powerful.
The graphics are the best ones I've seen on the GBA, and that's no overestimation. Not as good as the ps2 or anything but very good for a handheld.
The sound effects and music go very well with the game's visual effects, and I can't think of anything alse that goes this well with it.
Overall, this is a very good and well thought-out RPG, and well worth your mom's or your money. I don't care how you get it, if you have a GBA, and you love RPGs, you just gotta get Golden Sun