Pokemon Emerald is a remake and a combination of Ruby and Sapphire with a few extras. Great RPG series.
Pokemon Emerald is a more advanced version of the 2 games before it. Now, you can Explore the land of Hoenn in a more enjoyable way. It easier to catch Rayquaza in this game than it was in the ones before it. The Battle Frontier is now added onto the Hoenn Region, in which you go to after you defeat the Elite Four.
If you played both Ruby & Sapphire like I did, you know that only certain Pokemon were able to be captured in either Game. Only certain Pokemon were in Ruby and only certain Pokemon were in Sapphire. But in Emerald, most of the Pokemon are combined into one game, so it's easier to catch them all.
What's cool about the Pokemon cartridges is that they are colored according to which game it is. And in Emerald, you get a cool-looking, green, see-through cartridge. Pick this game up, if you're a Pokemon fan like I am.