It felt like :-\ to me
This was a nice, attempting to look graphically aesthetic version of websudoku. The problem about this is two things: how to use it and the lack of difficulty in game play.
Problem 1: By clicking the number you want to use to enter into a box, it takes too much time. It's a lot quicker if you allow the user to type it in.
Problem 2: The gameplay is too easy. It's recommended for someone who never has played sudoku. This is suitable as a tutorial, if it was more involved in letting the user know when they entered the wrong number into the tile. At least, there needs to be some levels of difficulty. I finished the puzzle in about 3 minutes. Fairly quick. (May be quicker if I was allowed to use the number keys on the keyboard)
If someone is going to play this over and over, the problem is that the sound is very monotonous and boring. This kills the interactivity when playing many puzzles over a long period of time.
I suggest this game to someone who's learning sudoku. With a few more additions, it would make a nice tutorial. Experienced sudoku players should use their magazines and websites. The interactiveness is ok, but a few additions, such as difficulty levels, hints, and different background music choices would make this likable.