I actually really love the difficulty in this game. I think it's at the perfect level. I'm so surprised they put out a game that's this difficult actually. The story was also really cool and I love the parallax scrolling and depth on the environments. The increased focus on horror is something I always wanted out of this series. I really liked how they weren't afraid to add some radical new elements into the story and have Samus speak again too. The (non-reused) boss fights were also really well designed it was fun having to learn the patterns instead of just tanking damage and spamming missiles like most of the other games.
My biggest problem with the game is the reused bosses... That and the map screen is a little too busy, it can be hard to read sometimes. Aside from that though... best game of the year possibly?