Pokemon Yellow served as the fully updated release of the original games.

This version was inspired by the anime causing it to have some changes to the game. GameFreak not only updated the main character model to resemble Ash Ketchum but also forced the player to take Pikachu as their starter to tie the two together.

It's believed that the success of Yellow Version is what led the Pokemon Company to making Pikachu a mascot of the franchise.

Introduced 100 new Pokemon

This game served as the first true sequel in the franchise featuring new pokemon, a new map, improvements to the combat system, a day and night cycle that had an effect on in-game events, and full usage of the new GameBoy Colors palette.

Served as a "director's cut" to Gold and Silver that only added a couple new features like both male and female playable characters, combat animations, and 2 new plots after the game is finished.

Introduced 135 new Pokemon

While the general gameplay remained relatively the same this was the first game to feature special abilities and double battles.

First game in the series to release on the GameBoy Advanced allowing it to be the most detailed game to date.

This game was a complete recreation of the original Pokemon Red and Green using the new game engine as well as featuring the newest mechanics and pokemon from the newer generations.

Much like Crystal, Emerald acted as a director’s cut to Ruby and Sapphire by being mostly the same game with changes to the story and an added endgame as well as improvements and balances to the gameplay.

Introduced 107 new Pokemon

Being the first game in the series to release on the DS it was by far the most advanced at this time. This game was the first in the series to use a blend of both 3D and 2D graphics and implemented many new additions such as a reworking to the move-classification system, online multiplayer, and the underground.

This game served as a director’s cut for the Diamond and Pearl games implementing improvements so game mechanics and changes to the storyline and endgame content.

These games were complete remasterings of the original Gold and Silver games featuring the newest game engine and mechanics as well as the addition of the newer pokemon, new areas on the map to explore and a new Pokewalker device that allowed you to walk your pokemon in the real world to gain experience and items in game.

Introduced 156 new Pokemon

This game served as a breath of fresh air for the franchise and included many new gameplay mechanics like triple battles, rotation battles, seasonal changes based on real world time and other mechanics to increase overall immersion.

Instead of being a third iteration director’s cut like all the generations beforehand this game served as a direct sequel to the story of Black and White. It featured a completely new story set 2 years after the original as well as making improvements on the gameplay and adding new features like the world tournament where you could battle trainers from the previous games.

Introduced 72 new Pokemon

Added many new features including new pokemon typing, the new mega evolution mechanic, trainer customization, as well as 3 new battle modes sky battles, horde encounters and inverse battles.

This was the first time the entire game was in full polygonal 3D. This was also the first generation to not get a subsequent 3rd iteration or sequel.

This was a complete remake of the Gen 3 games in the new fully 3D style as well as adding the newest of mechanics from X and Y and the new pokemon that have been added since it’s original release.

Introduced 88 new Pokemon including new region variants of pre-existing Pokemon

They also tried something new by replacing the Gym battles we’ve seen in every game until now with island trials which had trainers completing challenges before battling the leader.

This game served as the director’s cut to sun and moon but featured slightly more changes to the story than we saw in the past as well as new pokemon, new forms, and new gameplay mechanics that weren't seen in the original like the Ultra Beast wormholes.

Introduced 81 new Pokemon

Added many new game features like dynamax battles, gigantamax forms, camping and the first pseudo open-world area in a pokemon game. This generation also brought back gym battles but they implemented the challenge feature before the gym leader from Sun and Moon. It’s also the first time a Pokemon game got downloadable content, expanding the story and adding more new features after launch instead of releasing a third iteration.