Petals of Blood was officially launched by the Kenyan government in July 1977, in a show of the Kenyatta government's commitment to the principles of free speech. However, it was clear that the ruling elite and many members of the upper classes in Kenya were disturbed by Ngugi's harsh criticism of the established social and economic order. In reaction to the novel as well as to his play I Will Marry When I Want, after his release from detention in 1978 Ngugi was not reinstated in his job at Nairobi University, was arrested on trivial charges on several occasions, and received death threats.

Despite its status as a controversial work, the novel was received warmly by most readers and critics. An anonymous early review in Kenya's Weekly Review entitled ‘‘Ngugi's Bombshell’’ said that the Kenyan reader might feel as though Ngugi had been "walking all over your soul'' because of the way he portrayed the results of independence. The reviewer went on to call the work Ngugi's "crowning achievement'' but also noted the work's lack of humor and the people's unconvincing absorption in socialism. Joe Khadi, writing in the Daily Nation, another Kenyan publication, declared that "no writer has yet been able to expose the evils of such a system in as bold and fearless a manner.'' Other early African reviewers noted the novel's political impact, praised its narrative richness, and often criticized its use of Marxist principles.

Many western critics were also complimentary of the novel when it appeared. Christopher Ricks in the Sunday Times of London hailed it as "remarkable’’ and "compelling" for its presentation of political issues and innovative use of language. Novelist John Updike, however, writing in the New Yorker, was not as generous, saying that ‘‘Whatever else political fervor has done for Ngugi, it has not helped his ear for English.''

The novel has enjoyed considerable scholarly attention, and many critics have echoed the sentiments of early reviewers, acknowledging the novel's considerable strengths while pointing out its weaknesses. One persistent criticism has been that the novel's political message is too overt. In his discussion of Ngugi's writings, the scholar G. D. Killam, for example, says also that the novel ‘‘is open to the charge of political attitudinizing in places.’’ He says the call to right the injustices done to peasants and workers with colonial and post-colonial rule is treated at times with a heavy hand. However, Killam finds that the political attitudes and questions examined in the book are tempered by Ngugi's humanism, as throughout the novel his pressing concern is not with the putting forth of a political ideology but to draw attention to the degradation of human beings.

Other critics, however, have seen the novel's didacticism, or effort to teach and put forward a particular viewpoint, as detracting from its power as a work of art. Simon Gikandi faults Ngugi for his ‘‘authorial intrusiveness,’’ saying that it often forces situations and characters to fit into a "predetermined ideological position.’’ He says, for example, that the character of Joseph is not given any psychological development but emerges as a symbol of the ideals of reform that are central to the work. Gikandi suggests that this is a result of the novel being viewed by Ngugi as a means to ‘‘interpret, judge, and pattern the ever-changing African reality’’ and as a useful social tool, much like traditional oracles, whose main purpose is to confront people with meanings and values. Gikandi does not criticize Ngugi's purpose, but finds that the authorial voice in the novel is often jarring. David Cook and Michael Okenimpke also notes the false notes in the novel when putting forward a social and political message, but conclude that the novel is a "bold and powerful attempt to combine the intimacy of the traditional novel with a public rhetorical manner in a new and perhaps itself artistically and revolutionary amalgam in order to analyze social injustice and the human dilemmas it creates, and to mark out a practicable path to social change.’’

Critics have paid a great deal of attention to the complex narrative style of the novel. Many reviewers have viewed it as a powerful device, despite the author's occasional intrusiveness, as has been discussed. However, Stewart Crehan considers that the technique is confusing and that it is difficult to follow the ‘‘bewildering threads’’ of the narrative. He complains that with each new perspective, "an expected sharpening of focus does not materialize.’’ Crehan also criticizes the novel for its failure to live up to the standards of an epic, its stilted style with its use of stock phrases and "over-reliance of commonplace word,’’ and the muffled political message.

Petals of Blood has also been criticized by some feminist writers for its one-dimensional portrait of women. Elleke Boehmer, for example, points out that while most male critics and Ngugi himself has have pointed out the presence of strong female figures in this and his other novels, there is a strong patriarchal cast to his ideas. She says that his discussion of the rights of workers in Petals of Blood, for example, Ngugi seems to assume that true "work'' is the productive labor of men, and that women are excluded from this arena. Boehmer does point out, however, that Ngugi's female characters, such as Wanja and Nyakinyua, are pioneers in the field of African writing in English.

While many analyses of Petals of Blood point out its limitations, the general view by critics is that the novel is a significant work of modern fiction, and an important contribution to the debate about colonial and post-colonial conditions in Kenya. It is Ngugi's work that is seen as most representative of his radical political views and his humanist commitment to social reform.