American Beauty was widely considered the best film of 1999 by the American press. It received overwhelming praise, chiefly for Spacey, Mendes and Ball. Variety reported that "no other 1999 movie has benefited from such universal raves." It was the best-received title at the Toronto International Film Festival (TIFF), where it won the People's Choice Award after a ballot of the festival's audiences. TIFF's director, Piers Handling, said, "American Beauty was the buzz of the festival, the film most talked about."
Writing in Variety, Todd McCarthy said the cast ensemble "could not be better"; he praised Spacey's "handling of innuendo, subtle sarcasm and blunt talk" and the way he imbued Lester with "genuine feeling". Janet Maslin in The New York Times said Spacey was at his "wittiest and most agile" to date, and Roger Ebert of the Chicago Sun-Times singled Spacey out for successfully portraying a man who "does reckless and foolish things [but who] doesn't deceive himself". Kevin Jackson of Sight & Sound said Spacey impressed in ways distinct from his previous performances, the most satisfying aspect being his portrayal of "both sap and hero". Writing in Film Quarterly, Gary Hentzi praised the actors, but said that characters such as Carolyn and Col. Fitts were stereotypes. Hentzi accused Mendes and Ball of identifying too readily with Jane and Ricky, saying the latter was their "fantasy figure"—a teenaged boy who's an absurdly wealthy artist able to "finance [his] own projects". Hentzi said Angela was the most believable teenager, in particular with her "painfully familiar" attempts to "live up to an unworthy image of herself". Maslin agreed that some characters were unoriginal, but said their detailed characterizations made them memorable. Kenneth Turan of the Los Angeles Times said the actors coped "faultlessly" with what were difficult roles; he called Spacey's performance "the energy that drives the film", saying the actor commanded audience involvement despite Lester's not always being sympathetic. "Against considerable odds, we do like [these characters]," Turan concluded.
Maslin felt that Mendes directed with "terrific visual flair", saying his minimalist style balanced "the mordant and bright" and that he evoked the "delicate, eroticized power-playing vignettes" of his theater work. Jackson said Mendes' theatrical roots rarely showed, and that the "most remarkable" aspect was that Spacey's performance did not overshadow the film. He said that Mendes worked the script's intricacies smoothly, to the ensemble's strengths, and staged the tonal shifts skillfully. McCarthy believed American Beauty a "stunning card of introduction" for film débutantes Mendes and Ball. He said Mendes' "sure hand" was "as precise and controlled" as his theater work. McCarthy cited Hall's involvement as fortunate for Mendes, as the cinematographer was "unsurpassed" at conveying the themes of a work. Turan agreed that Mendes' choice of collaborators was "shrewd", naming Hall and Newman in particular. Turan suggested that American Beauty may have benefited from Mendes' inexperience, as his "anything's possible daring" made him attempt beats that more seasoned directors might have avoided. Turan felt that Mendes' accomplishment was to "capture and enhance [the] duality" of Ball's script—the simultaneously "caricatured [...] and painfully real" characters. Hentzi, while critical of many of Mendes and Ball's choices, admitted the film showed off their "considerable talents".
Turan cited Ball's lack of constraint when writing the film as the reason for its uniqueness, in particular the script's subtle changes in tone. McCarthy said the script was "as fresh and distinctive" as any of its American film contemporaries, and praised how it analyzed the characters while not compromising narrative pace. He called Ball's dialogue "tart" and said the characters—Carolyn excepted—were "deeply drawn". One other flaw, McCarthy said, was the revelation of Col. Fitts' homosexuality, which he said evoked "hoary Freudianism". Jackson said the film transcended its clichéd setup to become a "wonderfully resourceful and sombre comedy". He said that even when the film played for sitcom laughs, it did so with "unexpected nuance". Hentzi criticized how the film made a mystery of Lester's murder, believing it manipulative and simply a way of generating suspense. McCarthy cited the production and costume design as plusses, and said the soundtrack was good at creating "ironic counterpoint[s]" to the story. Hentzi concluded that American Beauty was "vital but uneven"; he felt the film's examination of "the ways which teenagers and adults imagine each other's lives" was its best point, and that although Lester and Angela's dynamic was familiar, its romantic irony stood beside "the most enduring literary treatments" of the theme, such as Lolita. Nevertheless, Hentzi believed that the film's themes of materialism and conformity in American suburbia were "hackneyed". McCarthy conceded that the setting was familiar, but said it merely provided the film with a "starting point" from which to tell its "subtle and acutely judged tale". Maslin agreed; she said that while it "takes aim at targets that are none too fresh", and that the theme of nonconformity did not surprise, the film had its own "corrosive novelty". Ebert awarded American Beauty four stars out of four, and Turan said it was layered, subversive, complex and surprising, concluding it was "a hell of a picture".
A few months after the film's release, reports of a backlash appeared in the American press, and the years since have seen its critical regard wane. In 2005, Premiere named American Beauty as one of 20 "most overrated movies of all time"; Mendes accepted the inevitability of the critical reappraisal, saying, "I thought some of it was entirely justified—it was a little overpraised at the time."
Currently, the film holds an 88% score on Rotten Tomatoes based on 181 reviews, with an average rating of 8.2/10; the critical consensus reads, "Flawlessly cast and brimming with dark, acid wit, American Beauty is a smart, provocative high point of late '90s mainstream Hollywood film." Metacritic gives the film a score of 86, based on 33 reviews, indicating "universal acclaim."