Really good
I really enjoyed this game, and I actually liked the monochrome style. However, I have one problem...
Maybe I'm just blind, but did you actually label the weapons anywhere in game?
I mean, the Backshot, Missiles, and Laser are obvious...but for example, on mission 52 you suggest the "Wave Shot"...now is that the second weapon with the little bat-looking things that travel in a wave, the fifth weapon that I would consider a "Scatter Shot" but could certainly see how it could be called a wave gun as well, or the last weapon that shoots the triangles and then eventually the triangles plus the wavy bat things?
Otherwise, I don't have any big issues (not that naming the guns is a big issue). I think any game as long as this one gets repetetive, but you minimized it by adding the new enemies every once in a while, so yeah, good job.
My only suggestion (other than labeling the guns) is that instead of having you blow up and lose a life when you get hit, why not call the lives "Shields?" You could change the animation slightly so you look encased in a shield instead of blown up (you can even disable your ability to attack for the same length of time) and change the powerup from buying extra ships to buying a shield upgrade. Then it wouldn't feel quite as silly that an A-Fighter can take a couple hits from the same kind of bullet that completely destroys you in one shot.