My thoughts on the game:
I'd say it's the best 3DS title, but it can be very slow to get started and pretty narrative heavy. SM definitely had the more coherent and tighter script too, just saying that right away. If you like Lillie's story and stuff, great, and if you don't then there will be a lot of suffering to go through, sorry. I'd say that the boss fights and the pace of them are the cleanest they've been in the series yet, and they only fumbled by making Ultra Necrozma a postgame-tier fight dragged back to before the 8th gym or this region's equivalent of it and thus making everything else a bit lackluster at the end (still legendary though, don't get me wrong). They really should've kept this iteration of the exp system for the future games. Z-Moves are just OK, the regional dex is godly and I love the poke pelago, cutest thing ever and the best miscellaneous feature GF has made which is why I'll always be crying blood over its removal.
My personal opinion? USUM is better than HGSS, XY by a country mile, B&W, RBY, FireRed, and Platinum, but about equal with Emerald, Crystal, SM, ORAS, and BW2. Feels like one of the games that was grasping at the idea of "the perfect pokemon game". Could pluck a lot from it, discard some yucky bits and remix it with other stuff to find that kind of hypothetical game.
This is gonna be the last playthrough thread from me for the year, and I'm on the fence about doing the switch games (especially since I'd have to pay extra money for games I might not necessarily like for the "full experience"). But I'll cover Rainbow Rocket before I say the playthrough's over.