When it was published in fall of 1971, many critics did not like the novel's loose plot and the scenes of drug use; however, some reviewers predicted that Fear and Loathing in Las Vegas would become an important piece of American literature.
In The New York Times, Christopher Lehmann-Haupt told readers to not "even bother" with the novel, and that "what goes on in these pages make[s] Lenny Bruce seem angelic"; however, he acknowledged that the novel's true importance is in Thompson's literary method: "The whole book boils down to a kind of mad, corrosive prose poetry that picks up where Norman Mailer's An American Dream left off and explores what Tom Wolfe left out".
As the novel became popular, the reviews became positive; Crawford Woods, also in The New York Times, wrote a positive review countering Lehmann-Haupt's negative review: the novel is "a custom-crafted study of paranoia, a spew from the 1960s and — in all its hysteria, insolence, insult and rot — a desperate and important book, a wired nightmare, the funniest piece of American prose"; and "this book is such a mind storm that we may need a little time to know that it is also literature . . . it unfolds a parable of the nineteen-sixties to those of us who lived in them in a mood — perhaps more melodramatic than astute — of social strife, surreal politics and the chemical feast." About Thompson, Woods said he "trusts the authority of his senses, and the clarity of a brain poised between brilliance and burnout".
In any event, Fear and Loathing in Las Vegas became a benchmark in American literature about U.S. society in the early 1970s. In Billboard magazine, Chris Morris said, "Through Duke and Gonzo's drug-addled shenanigans amid the seediness of the desert pleasure palaces, it perfectly captured the zeitgeist of the post–'60s era". In Rolling Stone magazine, Mikal Gilmore wrote that the novel "peers into the best and worst mysteries of the American heart" and that Thompson "sought to understand how the American dream had turned a gun on itself". Gilmore believes that "the fear and loathing Thompson was writing about — a dread of both interior demons and the psychic landscape of the nation around him — wasn't merely his own; he was also giving voice to the mind-set of a generation that had held high ideals and was now crashing hard against the walls of American reality".
Cormac McCarthy has called the book "a classic of our time" and one of the few, great modern novels.