Pretty good game, once you polish up the programming a bit it will be great.
I did have one match where I started with negative junk. I am not sure if this is a design feature or a bug. I died while building something the round before, and I believe it probably had something to do with that.
On one other instance, I had 37 junk, when I attempted to build it told me that I needed negative one junk. When attempted to build about 10 seconds later it worked. I might have been seeing things, but I am pretty sure that is what it said.
A small grace-period when probes spawn would be nice. I had one spawn within about 30-40 pixels and took damage immediately.
Wouldn't mind a bit of a glow on the probes at night as well. It was hard to locations of new probes when they spawned. I am so-so on this opinion, but at the very least you should weigh the options.
A small health bar or notification for the turrets would be nice, it was hard to tell if they were damaged.
Like most of the others said, tool-tips would go a very long way to improve the game-play.
A few other thoughts in the form of pictures:
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