The Island of Doctor Moreau is an example of what would be called science fiction today, but that genre was not widely recognized at the time Wells was writing. The term "scientific romance" was somewhat more well-known, and it is in many senses more fitting for the novel. Romance in the 19th century did not necessarily refer to books about love. Rather, it referred to books featuring heightened emotions and dramatic plot twists, often as they related to political questions and nationality.
The Island of Doctor Moreau is a scientific romance first because it offers a picture of the world as it might be if a scientific innovation (vivisection) introduced a whole new world order (a world where animals can be turned human, speeding up the process of evolution). This is the piece that's recognizable as science fiction. The novel is a romance because it uses extreme situations and extreme emotions (especially horror) to urge the reader to reflect on Victorian society. The dramatic plot serves not only to entertain, but also to convince readers that strict Victorian laws and morals provide a false sense of human superiority over animals.
The novel raises especially important political questions about race and colonialism. The conversation about human superiority over animals was frequently mapped onto the ideology of white supremacy, something that Victorians were accustomed to as a justification for colonization of other countries. Wells does not outright condemn colonialism, but he does use horror to problematize the idea that any group of humans is more "civilized" than another. Rather than pushing back against racist stereotypes about people of color as animals, Wells instead suggests that "civilization" does little to curb the animal instincts of anyone, including white Europeans. Many passages in the novel read like extremely racist passages from travel narratives, in which white European authors describe so-called "exotic" colonial societies. This is not because Wells condones the attitude of European society's inherent supremacy, but rather because he wants to impress on the reader that Prendick and other Europeans are far from immune from the possibility of assimilating into these "exotic" societies and behaving in ways that horrify European sensibilities.