The only Pokemon game I've ever played was Emerald on the GBA. It was pretty good. Are the games still like this gameplay-wise or have they changed a lot?
gameplay-wise it's pretty much the same. but there have been many changes too (e.g. mega-pokemons, ev training is so much easier, etc)
If you look at the main story, and the main game, it is almost exactly the same. Although they eventually introduced wifi (Diamond/Pearl/Platinum–the next series from what you played) and now there's a broad competitive field that is almost completely different except in concept. Some people think that the competitive feature kills the game because there's such a wide variety of variables that some see it like work and unless you have a thing for legendaries or pseudolegendaries you probably won't get to use your favorites, but some think it gives more value in that it adds a strategy aspect and offers bragging rights.