I love the beautiful and simplistic graphics! Very cool stuff!
Also not sure if it is a bug, but tapping the left and right arrow keys moves me much faster than holding them down. Wasn't really able to get around unless I did that.
That's intentional so that you can play with the movement speed better, and it also makes you more aware of the momentum ;) I started with the momentum theme and then incorporated the mutation one when I realised the theme had changed.