Sudoku is a board matching game. 2 board sizes: 6x6 y 9x9. 3 difficult levels: easy, medium, hard. You can play with numbers, letters, symbols and images. One or two player modes are available (in the same PC by turns),and you can save your records. Version 2 adds three new games modes: Crazy, Shadow and Guided.
Plenty of options. I like the number panel close by on the right AND the "correction" button!
Cons
Numbers are hard to read (background is too close to number's color & shadowing is just more confusion); areas are highlighted as the mouse moves and is very distracting (I already KNOW which areas are possibilities - should be available as an option on the Easy / beginner's games).