>>52841749TL;DR - try HGSS and Legends Arceus.
HeartGold and SoulSilver are generally regarded as the best games in the franchise for a reason, they’re remakes of the Gen2 games.
Black2 and White2 are graphically the most impressive and are fun on their own merits, but when compared to previous games they just don’t have the spark. The monster designs being the main thing holding them back.
XY are the most undercooked games in terms of content and story development, and are disappointing to play as a result because you can see all the stuff that would’ve been cool to build on if they ever made a Z version.
OmegaRuby and AlphaSapphire are probably the slickest and most complete in terms of QoL enhancements.
Sun and Moon are linear slogs, but the gameplay shakeups breathe some fresh air into the stale gym challenge design. Ultra Sun and Ultra Moon are basically the same games with just UI changes and the ability to battle trainers from past games.
Sword and Shield are the most ‘culturally influenced’ in the sense that they took the most time and effort to Poke-ify the location the games are based on, but are bare-bones in terms of content and has the most nonsensical plot. The dex cut also makes the game not worth it.
Legends Arceus is an excellent rethink of what a pokemon game can be (it includes things like overworld battling, pokemon attacking the trainer rather than the pokemon, stealth, actual open world exploration and crafting mechanics that fit the 19th century setting, and so on), but is very light on plot and is very repetitive. It also looks like a GameCube game.
Scarlet and Violet are the pinnacle of everything wrong with modern Pokemon, and not worth even considering. The only interesting aspects are the things they carried over from Legends Arceus.
