Sun / Moon are vastly different to any other Pokemon game to date (no gyms, Pokemon to call instead of HM moves, no national Pokedex and so on). I dont think been different is necessarily a bad thing, however I do feel we got half finished games not once, but twice.
Online functionality seems limited, for example when putting a Pokemon on the GTS you can't even type a message anymore like in Gen 6. The PSS system was really good in Gen 6 i thought, that's totally gone too.
No national Pokedex is a real shame if you ask me, it just doesn't seem right and gives little incentive to bring your past Pokemon to Gen 7.
I'm not personally a fan of the Zmoves either.
More than anything though what annoys me is the same game essentially got re-released a year later with some very minor changes. That would have been a really good chance to improve on Gen 7, not make a quick bit of money because the Switch game is not finished.