I finally defeated Bowser today and returned peace to our fair Mushroom Kingdom. Yea for me. After you finish the game, you can go back and play any level in any world that you completed earlier. I wonder if there's anything different the second time around? I want to go back and find all the secrets and stuff that I missed out on the first time through. This time I was basically just trying to get through each level as quickly as possible to get to the end, although I did get the "perfect clear" message after completing each world. Great game, my favourite of the Mario games.