Currently enjoying my playthrough of Ultra Sun. My team so far:
Gouki, the Terracat
Judy, the Lopunny
Navi, the Sylveon
Sea Unicorn, the Seel.
On the third island now, so far not much drastic changes. There is quite a few nice touches though to separate from the original titles. I really like Dulse and Zossie right now, I wonder how the Ultra Moon players are feeling about their Ultra Recon Squad? So far the biggest shocker for me was when the Wishiwashis were trying to school and become Totem Wishiwashi only for a Totem Araquanid to presumably destroy them and pop up in its place.
The game is harder than the first titles, however I'm half-half on it being fair, Akala Island was pretty fair challenges but when you get to Ula' Ula' the level spikes occur already, forcing me to level grind way earlier than previous titles. Kind of annoying when you don't use the EXP. Share because you like your Pokemon at similar levels. So I'm grinding my Pokemon to Level 33 before I advance through Malie Garden.