From 2004:
Even his most frankly poetic lyrics are best heard in tandem with the melodies that inspired them. Hence they occupy the same equivocal position as, say, Bernard Herrmann’s film scores, which are the products of a collaborative process and cannot be properly evaluated outside the context of that process. It is revealing that Mercer published no poetry, presumably because he felt he had no gift for writing it. Only in the crucible of collaboration did his talents manifest themselves completely….
Read the whole thing here.