It won't be a real sudoku game until the board can solve itself while rotating behind the title screen. (
shameless plug)
Alternatively, here's some suggestions:
Use shapes/colours instead of numbers, to confuse
Use a word instead of numbers, each letter being a number, so that you accidentally spell out anagrams
Add a sudoku solver. You input the numbers to start it off, it gives you the answers
Sudoku 3D. As in fancy graphics.
Sudoku 3D as in a 3 dimentional matrix - difficult to display, let alone solve
Sudoku 2D, the 2D remake of Sudoku 3D. You wouldn't actually release this, you'd just keep posting how close you are to finishing demo 4.