This is amazing for your first game! Congrats, and keep it up! Just a few suggestions- The instructions say left mouse button is used to shoot but that didn't work, pressing Space did. (Which I liked better.)
If you changed the fonts in the game it would look so much better, try dafont.com for free fonts! Also, I found that circular enemies weren't affected at all, I thought that was a bug but maybe that was just me.
Love the arcade style visuals and the audio. I think you should definitely stick with game dev :D