I beg to differ from Achebe's over-sensitivity. If anything, Heart of Darkness is a critique of colonialism through the eyes of the fictional Charlie Marlow. I didn't find an insult in the book except Conrad's drawn-out description of everything: the sun, the medical examiner, the accountant, and the carriers of goods from the ship to the station (i.e. the Africans who were barefoot and had splay feet). In terms of the poverty, hardship and underdevelopment level in Africa at the time, how else did Achebe want Conrad to describe the situation? Even women do not complain when the book has Marlow think this about his own aunt: women are strange creatures and live in a reality of their own.
Achebe's animosity has caused African writers to rebel against the English language, thus hampering its potential improvement on the continent. I think we should not follow his resentment so blindly. We should read Heart of Darkness for ourselves.