I had so much fun playing this. Amazing game!
It is not too difficult and you just need to take some time to get to the end. Controls are simple and responsive (mouse only). The hitboxes are very clear and defined. The bosses have openings between each attack and indicate before they attack. Saw grinding on alien ships is very satisfying. It feels like it was thoroughly play tested because the user experience is A+.
It was a little frustrating to lose all your power-ups when you died. I immediately died after I got all the upgrades for the final boss :( . The fights sometimes dragged out a little and then there were seemingly endless bosses/phases.