It was good, I've played this before in a giant sudoku puzzle book I bought a couple summers ago, and it was by far my favourite of all the puzzles.
Having said that, the gamaplay in itself was nice, but the visual could use some work. I see you said it's your first, and I'd say that was pretty darn good for a first. But if you ever choose to edit this version or remake it, I would say just make it more attractive overall- sleeker buttons, original backgrounds, etc.
Looks aside, this was a good game- I liked how you could check your numbers.