Lots of my friends think that Prince's music is old, but I think it's not only excellent but also an innovation.

Answer 1

The problem is in the second half of the sentence.

In a "not only ... but also ... " construction, you need to make sure the wording that follows each part is the same as the other. In this case, this is what's there:

not only excellent ("excellent" is an adjective)

but also an innovation ("innovation is a noun)

So ... revise so both are adjectives or both are nouns. How will you do that?

Answer 2

Lots of my friends think that Prince's music is old, but I think it's not only excellent or but also an innovation.