Quite good, when you take into account it was generated by a machine. Though, I noticed it was trying to sing also which sounded gibberish most of the time, if could generate only the instruments and not human voice, I supposed the model could improve from there.
It's similar to the case, of AI generated paintings, where the paintings is just representations of what data the machine learning model has already observed in the past and nothing else (in this particular case, the data can only observe the paintings of other artists). Hence why you cannot compare this to what an artist is able to achieve.
I guess, for this case is very similar, the AI is only generating what it has learnt from the other music generated by artists.