Pokémon Ruby (Red) and Sapphire (Blue), which was known as Pokémon Advanced for a while, will prove to be a new, exciting adventure in the Pokémon RPG series. There are going to be 100 more Pokémon joining all the other 251 Pokemon to make the land filled with 351 for you to capture. A big improvement over Red and Blue with only 151! There is going to be a new world to explore with new trainers, gym leaders, professors, and heros. Of course with 100 new Pokemon your gonna need a better Pokedex to catalog them all in, and thats what you get.
Because the game is for Gameboy Advance only Nintendo can really use the abilities it has, like shadows, footprints in the sand, ripples in water, and more like mist or fog. One of the biggest changes that will have an effect on how you play is that you can have two-on-two matches, meaning both trainers can have 2 Pokemon out at a time. Think of how effecient you could be with one Pokémon using Sunny day and another following with Flamethrower!
ANd of course with new games and Pokemon come new abilities, HMs, and TMs.

Overall I think Pokemon Ruby and Sapphire will be a lot different from the other games, and I am getting it right when it comes out!