Pokemon Sun is great, but Pokemon Ultra Moon magnifies the problems of the Gen 7 games. Ultra Moon is an expanded version of Moon, meaning it’s largely the same game, but with additional cutscenes… that you can’t skip. After playing Sun once, the cutscenes become very tiresome, and the new scenes don’t add much. All of the post-game content is really great, but it comes with the caveat of getting through the main game first. If you didn’t play S/M, Ultra S/M is the definitive version, but it’s a hard recommendation if you’ve already played Sun or Moon.