tl;dr from this post: people being overly picky about what their expectations are for a third game is where the hate is coming from, which is ridiculous lol.
From most of the people that I've spoken to, it amazes me how the #1 comment is "wow, these games feel so similar to SM!" as if any other third game wasn't already extremely similar to their predecessors in some manner. As I've said many times before on this forum, being a third game, USUM is bound to already bear extreme similarities to SM. Whether or not you're a fan of this practice of releasing third games that might as well be DLC is subjective and a subject for another time, but here we are anyway playing the same kind of third games that Game Freak has developed since forever; nothing has changed in that regard, really.
Another part of it is because the "new gen hype" is starting to wear off for some people. When SM was announced, it got a lot of people really excited for Gen VII because it felt like a breath of fresh air from your traditional Pokemon game. There was a lot of hype around the new Pokemon, a lot of hype around the new features, things like that. Of course, over time, hype is bound to wear down, and then people start seeing things in an unnecessarily overly analytical light. For some reason this tends to be The Thing around when third games are released and then people somehow start to appreciate them like years later which is kinda silly to me but w/e.
Third games, to me, have always been about improving the little things here and there, as well as adding a more enjoyable post-game experience. That was what Crystal was about, that was what Emerald was about, that was what Platinum was about and that's exactly what USUM is about. I don't think USUM is meant to be a complete overhaul of SM in any sense and I'm not sure where people got the impression or expectation that it was somehow supposed to be.
But don't let people's hate deter you from enjoying the games, really! USUM are my favourite pair of third games, simply because SM were great enough games as it is (sans post-game) and USUM improved upon that experience. I've liked what they've done with Guzma and Lusamine's character compared to SM, I liked the plot changes, the small changes to how trials are done are really nice. I'm already heading into the E4 and I genuinely cannot wait to challenge Rainbow Rocket. I can't wait to go into Ultra Wormholes and get shiny Pokemon and catch legendaries! Mantine Surfing is extremely fun, Roto Powers are REALLY useful for early-mid game grinding, and the difficulty curve is much appreciated.
I mean that by the way; I genuinely had a lot of trouble with some of the newer Totem Pokemon compared to SM! Game Freak got the difficulty aspect right this time around -- they've made Pokemon games appropriately (key word here) challenging while keeping them whimsically fun at the same time. I know I would certainly do Trials any day of the week compared to boring Gym Leader puzzles lol......
By no means are USUM a perfect pair of games, but really, can you genuinely say that about any Pokemon game ever? If you enjoy it, fuck what everyone else thinks about it, that's the truth. Just know that you're not the only one that loves these damn pair of games, because you're not.