This game fits the theme and I enjoy the gameplay. But there are a few things i feel like hold the game back.
The entire game feels very slow especially in the first couple rounds. I would suggest simply lowering the health on everything so levels dont take as long. Another thing is that choices dont feel very meaningful. Ship construction is super straight forward and the player only has input in the ship's shape. I suggest having it so the player gets a choice on like one of three ship parts to get at the end of each level instead of being stuck with the static choices the game gives.
On the positive side i really dig the art. Its very simple and cutesy yet effective for what youre going for (I especially like the fist weapon for the ship). The variety of ship parts makes it fun to discover new combinations and looks for ships.