Pokemon does it again...
It's amazing how, even though the core of Pokemon doesn't change, each region is fun and new. Hoenn, the region in particular, seems to have troubles. Two conflicting teams, Team Aqua and Team Magma, have their own goals in Hoenn, and it involves a colored orb and a legendary Pokemon...
In Ruby version, your mission is to become a Pokemon master. Starting from a small town, you'll battle Gym Leaders, including your own father, in order to gain entry into the Pokemon league. However, you must do something else; Stop Team Magma from awakening Groudon, the Continent Pokemon!
Groudon weighs a ton, has rediculously high Attack and Defense, and is overall a cool Pokemon, but even the hot-headed Team Magma has their troubles, and by the end of the game, everything goes awry.
The game's overhauled battle system, introduction of abilities, natures, contests, and a re-done Effort Value system makes you Hoenn experience one of the best RPGs the GBA has to offer.
It falls a bit short in terms of replayability, though. After you beat Steven, Elite Four Champion, there's not much to do. Battling friends is a hoot, though, ecspecially in great, full-color 32-bit. And the game's compatible with Pokemon Diamond and Pearl, so you can transfer your monsters to Sinnoh once you're done.
Overall, if you're looking for a GBA RPG that's great for kids, Pokemon Ruby is a good start.