Personally, I'm hyped. Pokemon Black 2 is one of my favorite games of ALL time, and my second Pokemon game ever.
I freaking loved everything about it, and it's one of the most nostalgic things for me ever. Assuming Ultra Sun and Ultra Moon follow a similar twin-version sequel format, then I'm excited.
I really appreciated how in BW2, you could see the affect you had on the region, from major characters to even really small-time, nameless NPCs (like the Castelia Cone person). I'd really like to see that in Ultra Sun/Moon, assuming they go the sequel route.
And if it IS a sequel, then I'd be hyped to see how the Alola region has changed. It'd be pretty cool if the Pokemon League system took place (as implied by the spaces reserved for future gyms), with traditional Gyms taking place instead of Trials and the Captains becoming Gym Leaders. And speaking of Gym Leaders, it'd be pretty cool if Guzma became the Bug-Type Leader for Po Town, with Hau becoming the Psychic Type Gym Leader (due to his Alolan Raichu), kind of like Cheren from BW2.
Additionally, it'd be cool if we got more lore for Marshadow, and had the generally-background characters Kahili, Ryuki, and Tristan. Obviously, more Ultra Beasts would be great and maybe we could catch up on Lillie, Gladion, Lusamine, and Mohn and see what happened to them.
It'd be cool if they did a similar thing like with Red where the Champion in Ultra Sun/Moon is the player character from before, but this time masked and disguised (so as to not set a definitive appearance), and kept fairly mysterious; with Nebby naturally being their leading Pokemon.
On another note, I've looked at the Ultra Legendaries and they remind me a lot of this theory I saw online about how Necrozma could split up into multiple pieces and act as a sort of armor and/or enhancement for Solgaleo/Lunala, and it seems they were pretty close.
All in all, this is a must-buy for me (unless it's NOT a sequel... then I might hesitate, but maybe not).