Had some great features. 16 gyms is controversial, but I like it, and gym leader rematches too. Also, Battle Arcade will always be my favorite Frontier/Subway-type facility. I'd like to see all these make a comeback.
I'd also like to see backwards tradability between 5th and 6th gen. Something they should have always had. I understand the disconnect between 2nd and 3rd gen, but honestly they could have found a work around for the ivs and simply reset the evs to get rid of those conflicts.