Villagers moving out on their own, definitely, and them just plopping their houses down wherever they liked. ;; For a while I appreciated the randomness of it, but sometimes they'd pick a really inconvenient spot, and I eventually started laying down patterns everywhere I didn't want them to be lol.
Also grass deterioration was the bane of my existence and I'm so glad it's gone. I liked having dirt paths in some places, but in others it just looked bad, but was sometimes hard to avoid walking over where the only available paths were narrow. orz Thankfully New Horizons just lets me put dirt pathing wherever I want, though I do miss the more natural edging (and can't be bothered to use custom patterns instead).
The inventory is also brutally small, even with the added storage option, and it's rough not being able to see your items, only the names when you tap on them.
I'm at the point where the extra museum exhibit rooms are just my external storage units now.