1: The difficulty. Gyms have full squad of six along with their field effects makes you use strategy to defeat them.
2: The evil team is actually evil. Not "Let's try to expand the land/sea for the good of the people" or "let's start up our base in one of the most obvious places in the region" No, team meteor is a group of motherf'n savages.
3: Story. As in most PKMN hacks, the story is far better than the original games, but Reborn blows everyone out of the water (literally, the water is f'n corrosive, you can't even get in it). Dark and mature themes across the entire game and it's probably hat most people would like to see in a PKMN game anyway.
4: Logic. Toxic air + Fire = KAAABOOOM. If I'm underwater, I shouldn't still be wrecking with a blaziken. (Still waiting on the EQ + Cave = IMMINENT DEATH to be slightly altered)