Maybe try making a game there isn't already 50 million ways to play it.
Sorry, but Really!? You expect a game that is also in every single newspaper in the world and has a puzzle book on every single book selling stand to do really really well because why? You launched it and sent it to a few app review sites? That's not all it takes to advertise something, there has to be a reason for someone to choose your game over the 50,000 other Sudoku games. And looking at it, there really isn't.
While I enjoy Sudoku, the overhead of entering numbers is challenging on a phone. I've liked none of the ones I've used, and so far the best Sudoku interface I've used is the one that was stock on my Nook Color.
Even with that, I find still I often find it refreshing to do on paper, as there's less interface annoyance in most cases.
I haven't touched a sudoku in a few years, but I went through a phase where it was interesting.
I developed a system with dots and sometimes little numbers (I think? I don't even quite remember it now) to track the possibilities that worked really well -- I could do advanced puzzles in pen, without ever guessing and being forced to backtrack.
Sudoku online was broken for me, though, because I couldn't use my method.
Pen/paper is a great interface for Sudoku -- very fast and flexible. Are there actually virtual interfaces that beat it, or is the only advantage portability (I'd have my phone at the doctor's office, but I'd probably forgot to bring a Sudoku book)?
I watched the video for this app -- is there support for any method of tracking number possibilities in a given square, or is the only option "make a reasonable guess and see if your score goes up or down"?
The latter is all I saw, and that's a horrible way to do Sudoku, no matter how pretty the graphics are.
It's interesting as a logic puzzle, not as a guessing game.
Most Sudoku apps I've used in the past had a notes system like the one you described. It's not that unusual of a system, I think it's a fairly normal way of doing things.
Sorry, but Really!? You expect a game that is also in every single newspaper in the world and has a puzzle book on every single book selling stand to do really really well because why? You launched it and sent it to a few app review sites? That's not all it takes to advertise something, there has to be a reason for someone to choose your game over the 50,000 other Sudoku games. And looking at it, there really isn't.