Super Skelemania isn't exactly the biggest game that's ever been produced, but it's damn good fun and the art style is delightful. If you've got even a passing interest in either pixel art or Metroidvania games, you should check this one out. The hero is a very acrobatic skeleton and he is your means to bound around a complex little set of levels that will keep you amused for, well, a short period at least! It's free as well, so why not?