Still playing this from time to time. Just one of the finest pieces of homebrew out there!
Noticed something btw., in level 6 respectively you can make a powerup fall into water. It continues falling behind the water but is also visible on the tiles to the right a bit. Since it's impossible to get once it fell into the water, it maybe would be better just to remove it to prevent that a-bit-odd-looking scene. Lightning in water also isn't that healthy.
...and I guess it's common practice in Jump'n'runs just to keep the jump-button hold if that "re-jump on enemy" is supposed to be performed? For my feeling it should be reaction-based, i.e. you have to repress the jumpbutton just before you land on the enemy. In fact I always did it that way until I realised that I just have to keep the button pressed...