>>34521181>>34527057>>34527095>>34521305USUM, fundamentally, is a good game. If you went in without playing SM, you would have a good time. Alola is a nice region that I had a lot of fun playing though, but god forbid playing through it twice.
USUM's issue is that unlike Emerald, Platinum and BW2, it barely adds anything substantial to Alola. People were very vocal about their issues in the original SM, what with the mass amount of cutscenes, the lack of postgame, the general emptiness of the region, Festival Plaza being cumbersome, ect. USUM was GF's chance to change and improve upon these, much like how they fixed the heaps and heaps of issues in DP when transitioning to Platinum, but instead we got some story changes (aka more cutscenes to mash through) and a few added scenarios to flesh Alola out, but at the end of the day, USUM still suffered the exact same problems that SM did.
Couple this with GF promising "Ultra changes," a lack of new Alolan Forms, and the heavily marketed Rainbow Rocket postgame story being no better than the Looker quest in X/Y, and you can understand why people from /vp/ to reddit to JP forums were all pissed about how bad USUM was. There's nothing present in this game that can't be a DLC pack for the original SM. A game like USUM is simply not acceptable in the age of DLC, but Pokemon has enough die hard fans that people are willing to ignore these flaws, and GF walks away with a fat wallet that they put zero effort into getting.
With all this being said, Sonic Forces never made any huge promises and I've heard the character creator thing is actually pretty decent, so I'd say USUM is a bigger disappointment since it had much higher expectations and met none of them. A properly expanded Alola could've been amazing.