I enjoyed playing this and the flip mechanic was really interesting, especially how the ships on the other side showed up as shadows.
The bullet speed and overall controls felt responsive and satisfying, along with how quickly the enemies died; not too long, not too short.
I did run into a few graphical glitches sometimes when the ship was at the side of the screen right when the screen flipped to the boss, but it didn't happen every time and I was still able to beat the game.