First off, I love me some sudoku and I did actually beat it. (In a underwhelming time)
Isn't really anything to complain about, its easy to navigate and the sides adjusts properly to show which side I'm working on. Only thing I could think of playing on the PC, It might be nice to naviagte the cube with the arrow keys. Like : Left Arrow = rotating the cube to the side on the left.
But this is a pretty cool concept, think it would be golden on mobile.