Although I haven't played many 2D mario games(I had a Genesis, so I'm more of a Sonic fan), this game is just so great to play.
Essentially, it is a sequel to the origional Super Mario series of games. It's a sidescroller that plays just like the classic mario games. However, they also added new moves, like wall jumping, and new items. And I will go right ahead and say this, this game is just as good or better than any of the classic mario games. And that is pretty hard to do.
Now I only wish Sega would do a "New Sonic the Hedgehog", and go back to making classic style Sonic games.
Stompy's Revenge related: I'll be releasing a new demo tomorrow featuring bug fixes, checkpoints, and the new high score table.