Nice idea, really addicting, but a few things:
1. I love how the background is different everytime, and most of theme look cool, but some of them look really busy.
2. In comparision to the characters, the background colors look really un-modern, if you know what i mean. Maybe make them more "neon".
3. You can easily improve the appearance of your game by using a different font than arial. Just go to e.g. Google Fonts and download some cool and more unique looking fonts.
4. And most importantly: Turn down the difficulty a bit!
I hope the feedback helped you, it would be nice if you could check out my submission too. :)