From the beginning I was wondering wtf was wrong with the controls, I knew there was something. At first I thought it was maybe lag, but then I noticed it was just when moving diagonally, but not always. Then finally during the first boss level I figured out that it was while I was moving diagonally while shooting... but not always.

Later on during that boss level I figured it out: You can't shoot while you're moving diagonally, except when you're moving up-right or down-left.

Unless you're going in those two specific directions, you either won't be able to shoot while you're moving diagonally, or you won't be able to move diagonally while you're shooting.

So the controls are really bad.

I was wondering why no one else was mentioning this, but then I tried it with wasd instead of arrow keys, and the glitch was fixed.

Anyways, too tedious/difficult for my taste (at least relative to how enjoyable it is). The upgrades are way too weak and boring.