Maybe I'm just not well versed in how Pokémon releases work. I assumed this was a sequel to Moon. But upon playing it, I could not tell you what is different between this and regular Moon. Aside from the in game title card having Ultra in the name, there is nothing I could point to that would definitively prove that this is a new version, and which couldn't simply be explained by me misremembering whether it was in the original Moon or not. (Aside from maybe the Nintendo Switch in your trainer's house, which was obviously patched in- it's the only explanation seeing as the 3DS was discontinued in like 2011 and they obviously didn't know about the Switch back then) From my standpoint I've essentially purchased a second copy of Moon and arbitrarily began to play it as though it were a different game.

For the record I like Moon. I mean, it was alright. I liked it at least enough to beat it, and enough to end up taking a chance on Shield. But after playing Shield, I realized I have zero enthusiasm for Alola region or its characters anymore. Now that I've been to superior Galar there is no going back. Hau might as well be a napkin scribble of a character that would go on to become Hop. And so on. Furthermore the Lillie subplot is also incredibly bland. That said if you have never played og Sun/Moon then this might be perfectly fine for you. It's playable, which is a pretty high bar to clear, especially for a 3DS game, and especially for a game with random encounters.