["Lenny"] looks to be about three-fourths dramatized biography and one-fourth recreated stage performances….
This one-fourth of the film is so brilliant … that it helps cool one's impatience with the rest of the film, which is much more fancily edited and photographed but no more profound than those old movie biographies Jack L. Warner used to grind out about people like George Gershwin, Mark Twain and Dr. Ehrlich. In movies, now as then, genius is principally defined by the amount of time spent dealing with disappointment….
However, "Lenny" is never very precise about what happened to Lenny or why….
[The] interviews are full of phony, simulated cinéma vérité-type irrelevancies in speech and manner that you never for a minute believe, any more than you believe that Lenny was just a sweet brilliant fellow who had some hard luck.
The movie makes no point of Lenny's terrible childhood or his ambivalent feelings toward his father….
Honey's affairs with other women, accepted and sometimes encouraged by Lenny, are touched upon so gently as to seem of little importance, as is Lenny's dependence on drugs….
Mr. Fosse, the director of "Cabaret," is also inhibited here. The production, photographed in glorious black-and-white, has a fine, seedy look but this, after all, is just more description. Was Lenny truly some kind of mad prophet or simply an accidental product of his times, which, though he died in 1966, were really the gung-ho nineteen-forties and the uptight fifties? It's to the film's credit that it raises this question, though it doesn't supply us with much information with which to answer it.
Vincent Canby, "'Lenny'," in The New York Times (© 1974 by The New York Times Company; reprinted by permission), November 10, 1974 (and reprinted in The New York Times Film Reviews: 1973–1974, The New York Times Company & Arno Press, 1975, p. 296).