Pokémon Ultra Sun & Ultra Moon

This isn't as good as 2D Pokemon but I still feel like this is pretty damn underrated and easily the best 3D Pokemon. But I get it, it's really handhold-y and there are too many cutscenes and Rotom won't shut the fuck up with his sad glowy game-breaking eyes. Also Sun and Moon were clearly unfinished and this is really just the completed version of the game sold at full price again (which is shitty business). But I still love all the little side events that give a sense of personality to the world, Rainbow Rocket episode, and hunting UBs. Totem Pokemon are good bosses (better than most gym leaders in other games) and the level curve is pretty decent due to the adaptable experience gain (which should just be a no brainer moving forward but nah). Has its fair share of issues, but I feel like gen VII had an ambition to them that gens VI and VIII sorely lack and these will be at least partly re-evaluated once we get a couple more crappy games and realize that yeah, these were actually kinda tight.

It's not worth the asking price as an upgrade to Sun and Moon. However, if you haven't played S/M, this is the version to go for if the difference in price is reasonable to you.
US/UM's best addition is the new eighth trial, which is just a boss rush. Actual battles against the trial captains were sorely missing from vanilla S/M, so they're a welcome sight. Second place goes to the new patch of grass at the base of Mount Lanakila, so you can catch some ice-types much earlier in the game.
US/UM's biggest flaw that isn't directly inherited from S/M is the two big difficulty spikes near and at the end. The battle against the box legendary is ridiculous, and you can't just throw a master ball and be done with it. The final battle against Giovanni in Episode RR is also far harder than anything around it.