This game is great! Great replay value and lots to do.
In each of six worlds, there are eight episodes (or levels) in which you complete the various challenges to earn Shine Sprites, the source of light and power in Delphino Island which you need to collect to restore peace and harmony to the Island.
Your Rival is Shadow Mario, who looks exactly like you (save the fact that he like a shadow all over), and who is creating the chaos in Delphino Island. He has a "magic paint-brush" which he uses to paint goop and graffitti all over the Island. You use FLUDD to clean this mess up, as well as to help you get around. There are four nozzles, the squirt nozzle to, well, squirt, the hover nozzle to hover in the air for a short time, the Turbo nozzle to speed around Delphino Island, and the Rocket nozzle to get you to high places.
It is not so easy that experienced gamers will find this game a pushover, and is challenging for all. There is much to do in this game and will last you a couple weeks (1-3) the first try and after another week or two you will probably want to play it again, and maybe one more time after that, giving it good replay value. It has six different worlds to explore, which each provides much entertainment for all.
There is no doubt this is a solid, fun, and good game for all to play.