What are the most common praises and criticisms of the novel?
Clarke is often praised for his astute irony, his literary pedigree, and his compelling plot. He breaks with many tropes and conventions of science fiction in order to create works that are arguably more highbrow and realistic than other works in the genre. On the other hand, his narrative lurches awkwardly from small-scale encounters to the broader view of humanity. It also lacks realistic, finely drawn characters; it only has one major (?) female character, and she is laughably stereotypical. The tone is strangely scientific and precise for the subject matter. The Overmind is also criticized for being too vague and convenient, with its origins, source of power, motivations, etc. left ambiguous in a manner that suggests authorial laziness rather than specific intent.
What are the pros and cons of the Overlords' rule over Earth?
There are many positive developments for the human race thanks to the Overlords' rule. There is no fear, crime, ignorance, poverty, grueling labor, war, or racism. There is no animal cruelty, and people treat each very well. There is ample time for leisure and people work where they want and for as much time as they want. They can travel wherever they want and advanced technology has made their day-to-day lives easier. They can see the truth in history and no longer have to cling to religion or superstition. Unfortunately, there are issues as well. There is a declining interest in science and there is very little produced in the way of great art. Humans are rather stagnant, almost bored. They do not dream or strive. They wonder where humanity will go next, and what the meaning of life is.
What should we think of Karellen as readers?
Readers' opinions of Karellen may vacillate throughout the book, and indeed, he is a complicated character. At times he is easy to admire for his intellect, his clear affection for Stormgren, and his general desire to protect the human race from itself. However, along with his lack of understanding about art, adventure (like the burros), and curiosity, he has negative traits as well: he does manipulate Stormgren (as with the kidnapping), and uses tools of deceit and subterfuge in order to carry out the Overlords' mission. He serves the Overmind in an outwardly subservient fashion, but his real motivations are a bit more obscure. He ultimately takes the Children away from their parents and causes tremendous, suicidal grief. This may be in order to help humanity "evolve," but it is cold comfort.
Does the novel have a positive or negative message overall, and why?
This is a difficult question to answer, and may be completely subjective. On the one hand, the human race evolves to another, transcendent state of being. This is a tremendous achievement and honor; the Children get to join the Overmind, which is roughly the equivalent of God. They get to move on unlike the Overlords. They are able to move beyond their limited, sublunary experience and abilities. However, this is immensely tragic. Not all humans get to do this; it is only achieved when the Children arguably leave behind all that actually makes them human and become completely alien to their parents and to the last human man, Jan. It is achieved only through tragedy and deception. The human race is actually gone in the most literal sense. The Earth is destroyed. Clarke's passive and scientific tone don't help us decide the answer to this question, either: are we supposed to realize the tragedy is not a big deal, or are we to remain cold at the attempt to make us feel like it is an honor to join the Overmind?
What is the Overmind, and how is it portrayed in the novel?
The Overmind has long vexed readers and critics, who wonder exactly what it is and what its intentions are. Clarke left this ambiguous, so all we have are some clues. Jan is the only man to see it, but we do not know if what he sees is really what it looks like. He describes it as a mountain that alters itself and turns into a funnel. He doesn't quite understand what he is seeing but he knows he is afraid. The red eye also gives him the same feeling. As for what it is, even the Overlords confess they don't quite know. Given Clarke's permeation of the novel with Christian themes, it is easy to conclude it is a God-like cosmic entity, but that also seems a bit limited. It also has echoes of the Transcendentalists' Oversoul, defined by Merriam-Webster as "the absolute reality and basis of all existences conceived as a spiritual being in which the ideal nature imperfectly manifested in human beings is perfectly realized."