I like the music and the art, aside from the red hitboxes.
However I think at the beginning you speed up too fast and at the end you're speeding up too slowly. I think you should've gone for a logarithmic curve instead of a linear one. Like some constant times log(n) as n increases instead of some constant times n.
I'm assuming you're increasing speed by like move(speed); speed++; or something
instead do like move(Math.log(speed)); speed++;
if you catch my drift. The beginning is too easy and then it gets too much harder to fast.
Speeding up on a log curve would work better I think.