I liked the combo of FPS and tower defence, haven't played too many that do it.
I thought the art and sound effects were well done, the art might be a bit too quality for a sbig game, but the fact they're bug guys makes up for it a bit.
Though the shooting I think was fine for SBIG I do also wish it had a bit more oomph to it, or that maybe the shooting could be permanently upgraded, because the default attack value made shooting some enemies just feel tedious.
And I agree with the criticism that after a certain point there's nothing more the player can do with the towers, since it's easy to max out all the spots and then they can't be changed or upgraded further.
And also, a fullscreen default or option would be great, felt a bit awkward playing it windowed on desktop.
Overall though this was pretty cool, great work!