The gameplay is mostly unchanged from the previous games; the player controls the main character from an overhead perspective, and the controls are largely the same as those of previous games. As with previous games, the main objectives are to catch all of the Pokémon in the games and defeat the Elite Four (a group of Pokémon trainers); also like their predecessors, the games' main subplot involves the main character defeating a criminal organization that attempts to take over the region. New features, such as double battles and Pokémon abilities, have been added. As the Game Boy Advance is more powerful than its predecessors, four players may be connected at a time instead of the previous limit of two. Additionally, the games can be connected to an E-Reader or other advanced generation Pokémon games.
Source: Wikipedia, "Pokémon Ruby and Sapphire," available under the CC-BY-SA License.