iCloud Messages is long overdue. Using iMessages on iPhone, iPad, Mac and Apple Watch is a pain, especially deleting messages on the watch.
For those who manually manage their music library, it’s been hugely buggy ever since iTunes Match rolled out, and hasn’t gotten better with Apple Music. If you turn on auto-download on all devices, listen to a song with your phone and then sync to your Mac or PC, the playcount doesn’t update. You have to turn off auto-download, then sync the song from the phone to iTunes, or vice versa. Playlists sometimes get duplicated when edited in iTunes, iBooks syncing is always removing books, asking for updates to books that have been updated numerous times... iBooks worked better when integrated with iTunes.
Lots of nagging little things like this that never seem to get ironed out.