I enjoyed the game until up to the final boss. The boss is way too unpredictable and punishing that I just wasn't able to finish it. Some advice is that you can have indication frames of where the attacks will come beforehand so players can have more reaction time, I've died a lot of times just because the block dropped right above my head and there was no way of telling that it was coming. Another suggestion is you can have the boss fight be scripted instead so that the attacks patterns are the same every time you play through it, that way even if the boss is hard players can learn from past experience and get better and better, which can actually be pretty rewarding!
I also agree with OKda about being lost during the race on tracking who I was playing, but otherwise I loved the races and little story breaks in the middle. The controls feel good and responsive and the race levels are designed well. The art and music is also great. I wished I was able to see the final ending but I still had fun! Great job :)