Pokémon Yellow Version! Well, for Game Boy Color, at least. It is the part 3 to Pokémon Red and Blue Versions, I suppose. It has different and better art than Red and Blue, better sound, more colors, and more importantly, you start with Pikachu!!! Yay :)
In this game, you are a boy named...well, you get to pick the name, but the default name is Ash, and you are on a quest to become a Pokémon Master. To become a Pokémon Master, you must defeat all 8 Gym Leaders, beat the Elite 4 and your rival, and capture all 150 Pokémon in the process.