Graphics are nice. That is your strength. But game design is lacking.
There's a lot of issues you can fix to make it better.
1. I didn't know what the controls where until I look closely in the game description, it should tell me within the game. Also some people like to use AWSD for movement. Also you should allow left and right for movement too, not restrict to up and down.
2. It's hard to read all caps for font. You should only use all caps for titles or small block of text.
3. Some stuffs were a bit confusing. I didn't know until later that the lines were bullet counts. I didn't know the seahorse player was pretty much invincible which makes too easy. I can see you deduct only 1 point of score for every crash the enemy do to the player. It's a bit strange. Doesn't make sense. Normally you should have a health point. At minus score you still don't die.
4. Sometimes the bullets gets recharged to full.
5. When there's a few bullets left, when you hold space, the bullet sounds still alot but the bullets are a few. Need fix the sound, you should attached the sound only to the bullet and not space bar.
6. There should be more variety in what the enemies do. They are pretty much the same except how they look. There should be different levels, it looks like just 1 level, and press R to restart. Or even there should be variety in the single level, should start off easy and then harder and harder, and finally a boss fight.
7. Consider making the seahorse smaller, there's not much room to move around.
8. Consider making the game harder.
9. Consider making the enemies react to getting hit, for example, flash red and sound. Same for seahorse player.