Sudoku, on the PS3! Theres not a lot more to it.
The initial pack id completely free and contains around 16 puzzles, 4 of each difficulty. And four additional packs are available (each of which corresponds to a select difficulty) for $2.99 each, which can easily expand the total to over 500 puzzles.
Even if your not a huge puzzle fan, you should give Go! Sudoku a try! What do you have to lose? Well, besides the time you'll eventually spend trying to solve every puzzle within the time limit. :)