After the shortcomings of X/Y, Sun/Moon feels like an apology meant for players like me. First and setting the stage, the music is immaculate - the Hawaiian-inspired music is immediately memorable and a much better use of streaming music than the bland and boring music of XY, and having some excellent battle music and theme music on top of that is great.
Much of the other aspects of the game are like that too. The characters in this game are some of my favorites in the series and the story is quite enjoyable, and it really just feels like a refreshing splash after being starved of such things, like it seems so obvious you'd want these things.
I said that the game is memorable, but many of the routes and dungeons are not. I don't mind it being linear but I do think there could have been better dungeons.

The Pokemon themselves are mostly good, though I feel like the introduction of region forms may have overshadowed the regular new Pokemon themselves. Also, this is around when Masuda went full casual and made a bunch of Pokemon intentionally not very good to use. The Battle Tower is there and a few challenges here and there, and of course the Ultra Beasts and Guardians.

Z-Moves are on one hand a fun and mostly balanced mechanic that I really like, and on the other hand pretty obviously a sign that Pokemon was taking on the identity of Yo-kai Watch. The fact that they had to share space with Mega-Evos didn't help. Also, I also just plain forgot about the battle royal mode.

Overall though, I think Sun/Moon was a great time and closest to what I want out Pokemon than any of the other 3D Pokemon games.