Great game. Nice and complex.
Just a few nit-picky comments:
Either a larger screen or a less busy background or brighter colors or something to gve the battlefield more DEPTH. It felt like a high overhead shot but there was too much variation and detail in the ground if that was the case.
It might even be cool with a cannon-like gun instead of laser-like ones. Maybe an upgrade? Maybe self-destructing drones? Maybe put the health bar closer to the fort so that damage is more easily apparent (again, brighter color alerts would help).
Whatever. I need to play it more -- it's a keeper. Well done.