Just finished the main-game and post game this week after stalling on it due to how boring the game became due to the feeling of Deja Vu. Good god, I've never played a third version with such a horrible start before. It took 20 hours before the Aether thing started and I finally got hooked on it.
Found the new stuff OK, but I'll agree with everyone else and say that Ultra Necrozma is downright evil and cheap, almost on Battle Maison territory. His theme music is epic but when he outsped everyone I had (who were in their late 40s and early 50s) even with boost items, it just made me go for my level 100 Articuno from bank to fight him. And he would have OHKO'd that as well if it wasn't for the max affection my Articuno had acting as a Focus Sash of sorts. Still, Mind Reader/Sheer Cold is always a solution for cheap Pokemon bosses. I just got done with Leafgreen which had a lot of evasion spam problems but even that game never got to this level of cheapness, so I wasn't happy with it, especially since the rest of the game felt perfectly fine when it came to the difficulty.
Post-Game story was OK, but still stupidly short and it felt even shorter than the UB hunt I enjoyed from OG SM. I don't think Gamefreak knows how to make a proper Second Quest like the Frontier, Fight Area, PWT, or Kanto anymore. Still, I'm at the Battle Tree now and am taking full advantage of being able to use level 100 legendary Pokemon for the non-super modes, since in OG Moon I wasn't able to raise a good team due to the lack of EXP spots in that game, and the Bank update came out too late for me to care about using my old ones.