I honestly can't believe the developer put this on hiatus at all. The game mechanic, in my personal opinion, is the best since Portal. I would totally fund something like this if I had two coins to rub together.
I like iamsuchanub's idea; the option to remove blood would be pretty swell. Or, maybe, you could retexture it so that the blood is all pixel-y, so it matches the rest of the game's style. That would be really cool.
This is okay...
but imagine if they'd put eight HOURS of work into this. It'd be longer and better looking (as it went along), I think. You hear that, developer? This is a nice concept to expand on.
This is definitely the best tower game EVER. As others have said, a speed up button is in order, and some more tower classes later on or in the sequel(if made at all). Great game!