Not bad
That was actually a good game. the game ran smoothly, plus the sprites were used well, making it a good expirience. It could've used a better design however in a few areas:
WALL JUMPS:
You mentioned that if you press up while hitting a wall, you'll do a wall jump. This is a good thing to mention, but, it should've been actually hitting the key, because you can hold the up key and jump. That makes it easy to get past the upwards hall, but, if you're jumping to get away from chasing enemeies, it's not good to suddenly be going back.
NORMAL ENEMIES:
I can understand Bowser himself being difficult, but his minions taking 3+ hits to down!? It's definitely a good thing that you made it so that the players stun the enemeies when the hits connect, because that would've been hell to fight 2. But, In my opinion, you should've had more enemies, but 1-2 hit takedowns.
LENGTH:
I did like how long the game was, it was the length of most Mario Stages, which was something I liked, but the length of it as a game was short. It needed more stages, but, other than that, it was good, not too long, not too short.
I did like the idea of it though, and it's a wonderfull game, but because of the parts I listed, It did have a few flaws. Overall it was a good game, but did need some stuff.