Wonderfully economical, both in development and in execution. I love how you made such fiendishly, finger-mashingly tricky levels from a few basic elements, and how versatile you made those elements.
I got to the end with $8.10, only losing a few cents on the last level. (I can't help but wonder if you get a different ending for finishing faster or with more money…?)
Also, I personally don't think this needed more levels, or at least not many more. The sassy spirit's dialogue helped to keep it enjoyable, but I would probably have gotten weary before the end if it went on much longer. This was an excellent example of achieving perfection when there's nothing to take away.
(MILD SPOILER BELOW)
That said, a couple of things seemed superfluous, or at least to hint at a different development trajectory: the slimes and the sword. The sword does nothing but break the doors at the end of each level and stab away at the harmless, apparently-solid slimes. Those seem like a hint that you meant to do more with the sword/enemy mechanic but didn't get around to it?
The movable platform was also an interesting touch, but it was so isolated I could interpret it as a one-off mechanic to reduce tedium. It's just how the slimes and the sword were so rich with potential yet so oddly useless that made them stand out.
The only other thing I didn't love was the conveyor belt; it was really hard to move on those with any precision, and it wasn't clear until my second playthrough that you could move backwards on them next to the spikes. (Which, at the time, would kill me if I touched the sides; I can see you adjusted that.)
Great work, this was a really fantastic game!