Well...
Opinion: This game was on the verge of being terrible. The brush tool was definitely used, but not very good, and easy to cheat, either moving the mouse with a fast movement, or doing the right click method many reviewers here have noticed.
Recommendations: Try making the cursor a small dot that is a color very separate for all the other colors. Even make the cursor flash if you must. Also, don't be afraid to use the line tool! Just as long as you thicken the lines nicely so you can't easily run over them. And, make the framerate at 120 so no matter how fast you move, you can't fly over a line. And add more color. This submission was extremely bland, and not very exciting. Also, place buttons that give you the ability to start and stop the music. Maybe even have multiple music choices. There are many tutorials that can help you with this kind of stuff.