It's not bad.
It's not bad, but there's definitely room for improvement. The floating island and race to the finish levels are a little overly difficult. Mostly because of the constant bees in the race to the finish level, and the lack of being able to control your character's jump (often way over-jumping platforms). So if you gave the player more control over their jumps like in the game it would probably fix both problems (seeing as the bees would be harder to avoid).
My only other complaint is that some characters actually change position when they turn around. So if you're standing at the edge of a cliff and turn around, the sprite will be displaced (possibly over the cliff, making you fall to your death). Some character sprites seemed to be less affected by this though.
Overall though, I think you did okay. Nice job. :)