I find the screen shaking effects to be very frustrating. I often find myself restarting a level several times just to accurately click on factories and not shift their positions before things start exploding. When combined with the glow effects, they can also make it difficult to tell whether a factory is producing hexagons or squares.
I would also greatly appreciate a volume slider or two.
I like that you get resources from your own destroyed units. It makes it feel far less punishing to be stuck on a level
I concur with what other folks have said regarding unit attack range upgrades mostly feeling like a trap, given the abundance of splash damage. It started feeling really bad around level 30, I think.
The ability to specialize certain factories is interesting, but the ramping costs incentivize pretty homogeneous upgrades.