The game is good! It’s noticeable that you spent a lot of time working on the artwork, and it really shows. Good job!
If you added some sound effects, I think it would be even better. You also have a lot of potential to turn this into something much more interesting, like a story about an astronaut who gets lost in the galaxy and has to fight different monsters, with different mechanics for each fight.
I hope you continue developing the game because I think you can make something really good out of it. Good luck!