If you haven't played either Ruby, Sapphire or Emerald, and wondering which to get, definately go for Emerald!
Its the first pokemon game with in-game cutscenes on the GBA I've seen so far, BOTH Team Magma and Aqua have to be stopped, and get this!! You actually fight Team Magma Leader Maxie and Admin Tabitha two on two with another trainer named Steven!! (Of course I haven't finished it yet, so more surprises for me are waiting to be found!)
Also, like in the Crystal Version, the pokemon themselves are animated! And you have places like the Battle Tent, Frontier, you still have the Pokemon Contests, they are in Lilycove.
What else… can't think of anything else right now.. ^^;;
Oh you can call other trainers if you get their numbers! Oh yeah and that shady guy called Scott… he looks shady at least.. but he's like some kind of stalker! XD
Thinking of exploring the Hoenn Region? Buy Emerald!!