/uj I don't entirely mind the linearity in Pokemon games, but what bothers me is the lack of optional areas and dungeons to explore. Johto had a good number of places you can go to and explore (the lower levels of Union Cave, that isolated section of Ruins of Alph where you can catch Natu, Mt. Mortar, Dark Cave, etc.). Hoenn had its ocean routes and the desert section of Route 111. Sinnoh had its various caves in Mt. Coronet, Solaceon Ruins, Fuego Ironworks. And even Unova, while definitely the start of Pokemon games being linear, had its fair share of places you could backtrack to find new places to explore and look around.

Kalos had Terminus Cave and that's about it.

Alola also had its share of optional spots, but they felt hella empty.

Galar I don't think had anything. The region was so streamlined with no detours you can take. Maybe there are and I missed them, but it annoyed the crap out of me that they made Escape Rope a key item there's only 2 caves (which are also hallways) you can utilize it in. This was what killed SwSh for me: the region feels like a giant glorified hallway with nothing to explore, and the wild area doesn't make up for it.