Conversation so far:
What were Georg Brandes's later writings?
Among his later writings must be mentioned the monographs on Soren Kierkegaard (1877), Esaias Tegner (1878), Benjamin Disraeli (1878).
What were some of his most important later writings?
The most important of his later works was his study of William Shakespeare (1897-1898), which was translated into English by William Archer and was highly acclaimed.

Question: What made that his most important work?
Self-contained rewrite: What made Georg Brandes's study of William Shakespeare his most important work?