Pretty fun, but probably just needs more time in the oven. I noticed that the enemy and technology trees were unlockable from the start, but they didn't do anything. There's also no indication of what the upgrades do or how much they cost, but for the implemented upgrades it's not hard to figure out.
The balance is also a bit off - it's pretty hard at first but once you have the triple spears and low gravity you can just click over and over again to create an impenetrable wall of spears that stops everything in its path. I think the late game needs a higher density of enemies and perhaps some new varieties of weapons.