I really liked the boss designs. They all felt and looked very unique. Having to target different parts of the boss at different stages is a nice feature. SFX and Music fit well with the rest of the game too.
For improvements, I had a lot of problems with the controls. I don't know if this is a bug, but my cursor moved when the ship moved. It was a constant battle between moving the ship and moving my mouse to keep the cursor in any one place. I'd also say the final boss is a bit too spammy. maybe lower the number of projectiles for that one.
Cool game concept though, good job!