Literary critic Harold Bloom wrote that Heart of Darkness had been analyzed more than any other work of literature that is studied in universities and colleges, which he attributed to Conrad's "unique propensity for ambiguity." However, it was not a big success during Conrad's life. When it was published as a single volume in 1902 with two more novellas, "Youth" and "The End of the Tether", it received the least commentary from critics. F. R. Leavis, referred to Heart of Darkness as a "minor work" and criticized its "adjectival insistence upon inexpressible and incomprehensible mystery". Conrad himself did not consider it to be particularly notable. By the 1960s, though, it was a standard assignment in many college and high school English courses.
In King Leopold's Ghost (1998), Adam Hochschild wrote that literary scholars have made too much of the psychological aspects of Heart of Darkness, while paying scant attention to Conrad's accurate recounting of the horror arising from the methods and effects of colonialism in the Congo Free State. "Heart of Darkness is experience ... pushed a little (and only very little) beyond the actual facts of the case." Other critiques include Hugh Curtler's Achebe on Conrad: Racism and Greatness in Heart of Darkness (1997).
Heart of Darkness is criticized in postcolonial studies, particularly by Nigerian novelist Chinua Achebe, who is considered to be "patriarch of the African Novel". In his 1975 public lecture "An Image of Africa: Racism in Conrad's Heart of Darkness", Achebe described Conrad's novella as "an offensive and deplorable book" that de-humanized Africans. Achebe argued that Conrad, "blinkered...with xenophobia", incorrectly depicted Africa as the antithesis of Europe and civilization, ignoring the artistic accomplishments of the Fang people who lived in the Congo River basin at the time of the book’s publication. Since the book promoted and continues to promote a prejudiced image of Africa that "depersonalizes a portion of the human race," he concluded that it should not be considered a great work of art.
Zimbabwean Professor Dr. Rino Zhuwarara broadly agreed with Achebe, though considered it important to be "sensitized to how peoples of other nations perceive Africa." In 2003, Botswanan professor Dr. Peter Mwikisa concluded the book was "the great lost opportunity to depict dialogue between Africa and Europe."  In 1983, British Professor Cedric Watts published an essay expressing indignation at his perceived implication of Achebe's criticism: that only black people may accurately analyze and assess the novella. Stan Galloway writes, in a comparison of Heart of Darkness with Jungle Tales of Tarzan, "The inhabitants [of both works], whether antagonists or compatriots, were clearly imaginary and meant to represent a particular fictive cipher and not a particular African people."
Fellow novelist Caryl Phillips concluded after a 2003 interview that "Achebe is right; to the African reader the price of Conrad's eloquent denunciation of colonisation is the recycling of racist notions of the 'dark' continent and her people. Those of us who are not from Africa may be prepared to pay this price, but this price is far too high for Achebe."