I think that this is best sudoku game available. Puzzles are selfgenerating so you have infinit nomber of puzzles, and if you quit you can continue when ever you wont.
Each Sudoku has a unique solution that can be reached logically without guessing. Enter digits from 1 to 9 into the blank spaces. Every row must contain one of each digit. So must every column, as must every 3x3 square.