Very nicely done and seems to have lots of features; very elaborate skill tree, with lots of variables.
I too would like a downloadable version (especially since I saw the Steam store page, but no demo (yet?).
2 quick comments:
1) not sure zooming in/out of skill tree has value, but right-click & drag works well enough; perhaps allow it a larger surface?
2) As more and more "tower types" are made available, perhaps a tooltip should be implemented to differentiate between the icons; they're pretty small on my laptop.
I hope you keep expanding the game as it shows promise! Had a good time playing the demo (v 0.3.2)