Did you draw the art by yourself? If so, I appreciate the effort, it came out pretty well
This is a good first game. Next time, I think some sound effects (I usually just download small asset packs from itch.io itself just to have it) would help. It is important that the actions in your game communicate well their consequences for the player. Shooting enemies or taking damage should be immediatly noticeble, and player-game feedback is really important
Looking for some tutorials or quick tips for game juice and feel might help you a lot. Game dev is very rewarding, so if you like it, don't feel discouraged. The only way to get better is to simply just make games. The more you make and the more you explore different mechanics, techniques and genres, the better you'll get. Don't be afraid to fail, just try to have fun and be proud of what you make :)