Sun and Moon (and by extension USUM) were great. A common criticism of Pokemon is that it keeps reusing the same 20 year old format over and over again. I do agree with this, but nobody mentions Game Freak changing it up with SM. The whole totem Pokemon thing is cool and fits thematically, and while the gimmick of the hour was just a lame attempt to bring Yo-kai Watch fans over to Pokemon (which didn't work Yo-kai Watch 3 is still the best 3ds game dammit), it could give some lesser-known pokemon a chance to shine. I'm also a big fan of the story in SM. The Aether Foundation is awesome and the battle with Lusamine-Nihilego was really cool. The Ultra Beasts are weird, but that's why I like them. There are just so many great ideas in these games, and it's really a shame that they went back to the gym format for SWSH.
That said, there are some bad parts. Festival Plaza is a good idea on paper, but it just ends up being annoying to use (hello showdown trailer). The dragon trial could've been so much better, especially with Vast Poni Canyon (the best "Victory Road" yet imo) leading up to it. MELEMELE ISLAND SUCKS. But even with those downsides, the games are still really enjoyable. I don't know why it was so disliked.