Wow, I loved the feel of this! Great job all around! For me personally, the difficulty is devastating, though. Once I got maybe a quarter around the loop before my opponent finished it. Just surviving was difficult for me, and even on level 1, the opponent was insanely fast!
I'm wondering how it would play if there was no AI opponent, just your own ghost (keep in mind, I never got far enough to play against myself). That might regulate the difficulty at a level where you're just trying to improve against your last instantiation. No matter how bad you where, you just have to do a little bit better. That might be fun?