>>35210218USUM is my second favorite mainline Pokemon game, behind BW2. Also SM was good but did have a very empty feeling afterwards, which I did not feel with USUM.
I loved the UBs, the Photo Club, the wormholes, Poke Pelago, and the bug types (overall the new Pokemon/Alola forms were largely stellar, and it had some decent uses of the fairy type). No HMs also a plus, and the lack of grid appealed to me. The myriad of small sidequests and extra little touches helped considerably as well.
Festival Plaza was inferior to the 2 predecessors, but still enjoyable enough and the Battle Agency was alright.
USUM had some pretty damn good singleplayer bosses, was pretty surprised when my Araquanid managed to barely survive U-Necroz's attack and counter with a Z-Liquidation, only to deal less than 1/4 health. Bulky and powerful.
I liked the story as well (if you didn't I\d imagine it hard to enjoy the game) due to the new antagonist and the lesser focus on Lusamine, despite enjoying her in SM enough, save for the mediocre boss fight.
Overall a solid 8.5/10, too flawed to give a top billing but genuinely one of my favorite gen finishers.