This is one of the only Mario spinoff/tribute/fan games which doesn't suck. Usually it's some horrible attempt at a platformer where it's not even clear the author even played the originals. To be clear, the official Mario games all tend to be very good, with few exceptions -- it's the fan/tribute games which tend to almost all suck.
So good job on actually staying somewhat true to the source material. It's not as smooth as the official games, but that's more of a nitpick.
That final last boss is unforgiving though. Like Dr. Wily in Mega Man VII unforgiving. I don't recall any of the bosses in actual Mario games being as unforgiving as that. Since the game does include references to Mega Man (and Metroid, Street Fighter, Mortal Kombat, Kirby, am I missing any??) I feel it's fair to discuss.