Very Good, just a few things
It's a very nice game, however there are a few minor problems.
The Scrolling screen makes the game rather difficult, especially for only one level. I would find myself falling off the edge because I couldn't switch back to Mario fast enough, or jump far enough.
Also, I was unable to find a "B" button, which would make me able to run. It could be there, but may not be included. Having such as a button would help a little with the gameplay.