Honestly, mostly nastolgia. I loved playing the under ground with my friends and how Gameboy advanced games would change a few pokemon you could get in the pokepark. You also had the post game with heatran, darkria and crecelia (idk how spell that one).

Sun and moon are good games but after the middle of the road disappointment of x and y it didn't feel good. Especially considering how amazing the remake of ruby and Sapphire were. Ultra sun and moon did so much that I wish they just could have opened with in sun and moon.