Deceptively simple at first, but the amount of upgrades you can have adds a whole lot to strategizing. AI on the units are pretty well done, haven't had too much scenarios where I feel like the unit I placed was doing something outside of what I expect. Also really love the take of tower defense where player themselves can do the attacking.
Not too sure if I am using the skills correctly, I don't think it does anything for me. I might have missed out what pressing E does when I was buying upgrades, so maybe showing tooltips when player mouse-over the skills/units icons would be great.
I had fun! Thanks for making this!