In my mind, the question is asking to assess what Tagore gave to Indian Literature translated into English. Part of what makes Tagore such a compelling figure in Indian Literature is that he is not writing in English. At a time when so many believed that English was right and indigenous forms of expression were wrong, Tagore pretty much invented the short story in Bengali. His embrace of both social realism and transcendent themes were all composed in his native tongue, making his contributions to the Indian literary canon powerfully compelling and highly significant. Tagore was also one of the first artists of a "globalized" world. This means that his contributions were even more significant because they spoke for a condition of Indians, as well as people all over the world. This was because Tagore had been exposed to literature that many in India had not experienced. Tagore integrated these artists' work into his own:
...other influences on Tagore were British colonialism .... Because of colonialism, he was exposed early in life to the literature of William Shakespeare, John Milton, and George Gordon, Lord Byron, who became his particular favorites, as well as the philosophy of John Stuart Mill and Jeremy Bentham. Other literary influences (Tagore read them in their original languages) included Johann Wolfgang von Goethe and Guy de Maupassant.
This ability to combine other literary voices into his own is what makes Tagore responsible for a giant contribution to Indian English Literature.