Addressing students at the Azim Premji Foundation in Bangalore, Karnad said since Tagore had an elite upbringing, his plays lacked empathy for the poor.
"… He sentimentalises the problems of the lower classes in his plays in a way that is almost condescending. None of his contemporaries would call him a great playwright."
He said he had a higher regard for playwrights such as Vijay Tendulkar and Badal Sarkar.
"Other than Rakta Karabi (The Red Oleander) and Dakghar (The Post Office), you don't hear of any of his other plays being staged," he said.
Tagore wrote three categories of plays: prose plays, verse plays and dance drama.
Reactions of intellectuals of Kolkata have been tempered.
Historian Rajat Kanta Ray, who is ex-vice-chancellor of Visva Bharati, said: "Karnad is entitled to his own opinion (but) Dakghar and Raktakarabi were internationally performed in the interwar period and after the Second World War."
Playwright Bibhash Chakraborty said: "Will it malign Tagore in any way? Ignore it."