It would be correct to say “How great is this music?” Although this is a question, it’s rhetorical and usually you wouldn’t expect someone to answer. It just means the music is great. You could also just take out the word “it” and say “How great the music is!” Also, you could just say “the music is great” The sentence you put isn’t correct because the structure is incorrect due to the word “it” I hope this helps you!