Great game; a sudoku for the 3 dimensionally minded. Couple of suggestions:-
1. Modify the colours with patterns to aid colour blind people.
2. Have a reset level
3. Have another introduction page showing the various nets; it's not necessary but if its not a term one has come across before it might be confusing.
4. Have a timer.
5. Different solid nets. I want a rhombitruncated icosidodecahedron in there.
 "Dynetzzle"){kind=icon}