I played the game and wasn't particularly fond of it. It is obvious that you've put some effort into it, but you're coming short of too many things to make it an enjoyable experience. You have to pay attention to the details. Your game is not very big, you are allowed to make it bigger, so use more than one soundtrack on a loop. A menu track, into sound effects, additional in game music tracks.
You need additional levels, possibly more than one difficulty.
The good:
+ Decent graphics
+ No visible programming errors
The bad:
- No cursor. You should have made a crosshair or something like that + another cursor for menus.
- Tame sound effect for shots and none for hits. In general too few sound effects.
- Oddly placed replay button. It should have been on the same page as "Submit score"
- Since you added medals, you should have added meaningful ones. Otherwise, don't.
- The enemies stopped spawning way before the timer ran out.
I can't give you a passing grade for this. I hope you will improve the game and submit it again.