FlowerSudoku is a nice sudoku game which offers multiple options for different skills levels. In case you don't know the game, sudoku is a puzzle game in which you need to fill a grid with numbers from 1 to 9, in a way that every column, row and 3x3 area has no repeated number. This game allows you to generate different puzzles very easily and it offers six difficulty levels to choose from, which vary in the amount of given numbers it has when you start a game.
All the games are timed, so you can keep a record of your best scores. However, you can pause the timer any time you want and the grid will be hidden, so you don't cheat. The program even allows you to create your own puzzles or you can copy those from magazines or newspapers to check their solution. A great thing that this game can offer is the capture option, which allows you to capture any sudoku game you find on the internet and copy it to the game, so you can play it there. If you are a beginner, the program also includes a feature called "Note all", which shows all the possible numbers for each cell.
In short, if you are looking for a complete and nice sudoku game to be entertained for a while, I really suggest that you may try FlowerSudoku.