Let's see... my very first GBA game was Pocky Rocky and Betty, which was friggin challenging for me, or I think I was just impatient.... I still have to get back and beat that. Favorite RPG so far was Summon Night: Sword Story. Saw the preview of it in Nintendo Power in Barne and Noble, and I instantly knew that was a game I would love, then I tried it, and not knowing it was an aRPG, it was my instant favorite handheld RPG. Klonoa 1 was great, never got around to two, I think I will now though since I can >.> Also, really loved Gunstar Heroes on the GBA, was really awesome to play. Really wish multiplayer was in it.
For some reason this thread seems more helpful to find good, unique, and fun games than the GBA essentials thread, lol. *goes off and searches for more information on some games mentioned*