The ships look really cool and and the game is quite fun to play!
First piece of feedback, the game is difficult from the start, there should be some scaling, maybe tied to when you kill an enemy causing more to spawn. For now it seems random and overwhelming.
Second, the background looks kinda odd because it has bigger pixels than the spaceships.
The ships are very verried in their movement and shooting patterns but there is a big difference in kill difficulty. I find it hard to kill the smallest ship as it is also the one that moves the most, but the big ones are stationary so way easier to kill. Even though their shots are the biggest they always travel the same path and so are predictible unlike the small targeted annoying ones.
Overall, fun game but too difficult too quickly and too short powerups or too few of them, they never overlapp which is a shame.