This game was by far the best Gameboy Pokemon ever!
First the storyline was not really tampered with but a different end mode in the battle frontier. In this mode you fight your way through a set of trainers with different specialties to try to finish that certain building. All of the buildings have different game modes, from normal single battles to trading in your Pokemon and using new ones. The new Pokenav makes finding people to battle easier and making it possible to fight with old gym leaders. Also, the contests are a great extra so that you don't get into a rut.
Another addition is that the graphics are upped o a whole new level, giving a almost 3 dimensional feel.
Though there is not much change from the previous game, it wasn't really necessary. Also, this game is a good buy even now because the story keeps going even after the elite four is finished. Which is not the case in newer versions.
All-in-all this game is great and definitely worthy of a 9.5 out of 10!