I admire the creativity on the bullet hell patterns, which doesn't seem to lag on my browser, so that's a good pro for you! One thing I have to mention is specifically on difficulty. Sometimes when passing through bullets, I get hit and that's normal, but since there's almost no invulnerability, I end up being damage thrice or even more. And also it doesn't seem as I could do more than dodging, some player empowerment would be interesting. The game is pretty neat though, great job!