I like the concept and the characters are silly and cute! That said, I died on the second stage way too much because one of the boss's attacks (the one that summons walls) would cause a huge lag spike! So unfair... But every time I died, I somehow had more cash than before, so I finally said "heck it" and just built a cube of guns which did the trick.
My main complaint is actually the dialogue - there's no way to speed it up at all? It moves so slow, I would dread starting a new game and sitting through that intro again.
By the way, if you buy fuel, but the fuel tank destroyed during the level, your fuel level stays increased. Is that a bug? Also after dying, you can still fly around and destroy stuff while waiting for the "delivery failed" text to go away, which is definitely a bug.