Fahrenheit 451's mood is grim, violent, and often dreamlike, such as when Guy slips into memories or is in moments of immense emotion. Readers might feel suspicious of what characters say; there is a good deal of uncertainty about who Guy can trust and what will happen next. The frequent violence and quickly paced plot also mean the novel is highly suspenseful. It's never clear which characters will survive to the end.
However, just as the tone is ultimately hopeful despite all the darkness in the book, the reader too may feel a hopeful mood by the end of the book. The novel suggests that an individual attempting to gain knowledge and think critically can leave a positive mark on the world.
Accordingly, Fahrenheit 451 leaves the reader with something like a call to action: read, think, and don't rely only on entertainment and distraction. Because the dystopian society has so much in common with the time period during which Bradbury wrote it, and even with our present-day circumstances, the call to action is even more compelling: the events of the novel seem not only possible, but probable. At the same time, science fiction and stylized descriptions alike make the dystopia uncanny and frightening.