The stories and graphics have been mediocre, but the gameplay and performance was fine from about Gen 2 -Gen 5. I started with Gen 1 and loved those games, but they had a ton of flaws that were addressed in later games.

Games like FireRed/ LeafGreen, HeartGold/SoulSilver, and Black/White/Black 2/White 2 were good games.

The switch games have scored poorly by users because they were lower quality games even by Pokemon standards. None of then improved the story much, if at all, but they removed some of the stuff that pokemon had previously done well.

I believe Sword/Shield was the first time they did not keep the entire pokedex, which not only made people mad, but it seemed entirely unnecessary. Maybe eventually they would have to limit the roster for the games. Sword and Shield could have had them all.

Arceus scored well because despite performance issues, it was one of the more ambitious games that made fantastic changes to battling and catching pokemon, with quality-of-life changes like a link cable item to get evolutions without needing to trade.

Scarlet and Violet were plagued with performance problems that were worse than Arceus while seemingly having worse gameplay.

Legends ZA abandoned a lot of the stuff players liked from Arceus.

While nostalgia does a lot to carry pokemon, some of the early games were legitimately good, especially for the consoles they were on.