The Tintin series starts and ends with different types of weakness. At the end of Herge's career the books are visually elaborate but lack the visual spontaneity that makes Herge's greatest albums so loved; on the other hand, at the beginning they are masterpieces of the comic-book serial form, but they are weaker in terms of plot. Until recently, the earliest of the adventures to be commonly available was Tintin In America, so there was a lot of interest among fans when first Tintin In The Land Of The Soviets and then Tintin In The Congo were republished.
Given the fall of Communism, the right-wing orientation of In The Land Of The Soviets attracts very little criticism now. In The Congo, however, plays on some readers' sensitivity to issues of colonialism, racism and animal welfare. To my mind, condemning this book on the third count is like saying that Jerry should be kinder to Tom. There is some merit to the accusation, though, that this book promotes ideas of colonial paternalism: the Congolese are treated sympathetically, but very much as gullible children. Also, they are drawn with curly hair and thick lips, which might itself be considered offensive in a comic strip drawn today.
Any responsible parent will want to flick through this book before handing it, or reading it, to his or her child, but while there are things here that should probably be explained by reference to their historical context, there is nothing here that I would personally regard as outrageous. Tintin does not mistreat the natives, and Herge's concern regarding the exploitation of indigenous peoples is clear from his depiction of Native Americans in Tintin In America (the next of the adventures to be published). Indeed, the book could play a valuable part in educating a child about how our views about Imperialism changed in the latter half of the Twentieth Century, but that lesson can only be taught to a child old enough to understand it.
This, then, is a secure purchase for those who enjoy Tintin. It's isn't a great entry point to the series: the best books for that are probably still The Crab With The Golden Claws and The Blue Lotus. Nevertheless, it is more than a historical curiosity.