Just one, and that's the type diversity, which ruined the whole gaming experience for me. I thought we were going to have an expanded Hoenn dex that wasn't just cross gen evolutions when they revealed Mega Evolutions to Pokemon who weren't present in the original Hoenn dex. But no, it's just the original Hoenn dex plus the cross gen evos, and despite getting your national dex after facing Kyogre/Groudon and encountering trainers from Victory Road using non-Hoenn native Pokemon, the Elite Four were still restricted to using Hoenn natives on your first encounter, thus having Pheobe, Glacia, and Drake using 2-3 Pokemon from the same family line on their respective teams. This has been the biggest problem in the older games, and they still didn't fix them when they remade them.