Same as the other two comments. The art is fine, but it appears to be unwinable in it's current configuration. Furthermore, there is no information on your towers or on enemy units, too few upgrades, etc. This appears to be incomplete.
One of the power ups makes your guys sit and spin instead of focusing fire. I could not remove this "benefit" once it was on my guys. Result: losing every battle. Sigh. Needs work.
New version has been uploaded that addresses freezing issues.