1. It's full of content story-wise, and I loved nearly all the cutscenes, as opposed to previous games where you basically just go through the motions. In fact, it's the best one yet imo (Outside of maybe BW2? The only one I didn't play, so can't say for sure), and I actually came out caring about several characters and their character development.
2. It's the most challenging one I've ever played. I gave myself a few minor handicaps though (Eventually turned off Exp. Share, Set instead of Switch, eventually stopped using Z-Moves) and eventually I gradually came across wild Pokemon and trainers, including random ones, that were a higher level than mine. If you're unprepared, getting wiped out actually is a possibility for once. The Totem Pokemon were a particular highlight, as they were actually pretty damn clever and challenging (usually) through their movesets, free stat boosts, and the ally Pokemon they call to help them out.
At any rate, it's my favorite Pokemon game yet.