Using my AppStore SEO tool (still in beta) I see you only appear in the results page of one popular search phrase "amazing sudoku"... http://www.straply.com/app/android/guru-mobile/empire-of-sud...
But some other Sudoku apps appear in the results of hundreds of popular search phrases... http://www.straply.com/app/android/genina-com/sudoku-free/so...
Perhaps you could try expanding your description to include more of the popular phrases related to Sudoku?
But the real problem is what everyone else has been saying. Sudoku is just too crowded.