Pokemon Yellow

This is the game that started the Pokemon series tradition of following up the first two games in a generation with a third game featuring additional features and improved mechanics. The core gameplay from Red and Blue has remained mostly unchanged, so I'll only be talking about changes, and you can go check my existing page on Red and Blue if you want more about those games.

Pokemon Yellow was created when the Pokemon anime was enjoying huge popularity, so this game was made to resemble the anime as best as possible while still relying on pre-existing games as much as possible. Thus, you'll find specific Team Rocket encounters modified to feature Jessie, James, and Meowth, gym leader dialogue and teams, and general Pokemon availability, changed to match the anime, perhaps most importantly, the addition of Pikachu as your only choice of starter. And the Pikachu given to you is special, refusing to stay in it's Poke Ball and instead following your character around the overworld and occasionally interacting with the world and with you. Your relationship with Pikachu will also grow over time, resulting in different and happier reactions when you talk with Pikachu, as well as special dialogue with a couple NPCs. It's such a fun mechanic, I loved seeing it back in Heartgold and Soulsilver, and am thoroughly disappointed that it never made it's way into any other games.

The other big change to Pokemon is the ability to acquire all three starters from Red and Blue, in various ways to emulate the anime. Charmander is given away by a boy who grew tired of him on Route 24, Bulbasaur is given by a girl in Cerulean City if your relationship with Pikachu is good enough, and Squirtle is received from Officer Jenny in Vermillion, provided you've caught 60 different Pokemon by that point.

Beyond that, most gym leaders and had their teams updated to match the anime, as well as buffing most of their levels by a bit, leading to some gyms being more difficult, while others can now be cheesed easily. The elite four remain mostly identical, but with rearranged movesets, and your rival is still the champion at the end of the game. However, because there's only one starter selection, your rival can't select the remaining one that has the advantage over your choice, so instead they are given an Eevee, which will evolve into one of three Pokemon depending on how you fare initial battles with your rival.

All told, I think this is a solid improvement on the original Pokemon games, and my personal favorite way to play the first generation of Pokemon games, and if you want to experience that generation, this is the game I'd recommend you play.