The bad news is the voice acting.
We really don't want to cast any aspersions on what looks like a truly fantastic puzzle adventure game, and we don't want to suggest that the game is in any way bad. But we just can't let voice acting like this go by without comment. Apparently, Nintendo wasn't able to solve the puzzle of where to find people who speak with British accents.
[Update: the trailer has shown up on Gametrailers, and has been added to the post.]