Hall of Fallen Foes is a pretty cool addition to the original game, I always liked browsing through enemies to learn more about them in games, and making it a sort of museum-like actual place is cool. Boss Rematch is also nice.
I hope they've kept a few things under wraps, subtle changes and stuff. I think they should have some DLC later that adds the Master Quest where they could add the Temple of Light that was originally cut and have you find the Triforce which wasn't in the original game at all (despite persistent rumors to the contrary).