Senses of Cinema has an article that says:
As a filmmaker, Tati has recurring themes (the leisure class, modernisation, children at play, mass entertainment), and his compositions seem as mathematically calculated yet spontaneous and vibrant as Welles'. His movies beg for purveyors of theory to figure them all out for us. Nothing against the theoreticians, but given a filmography that includes titles like Playtime and Parade, and films that make constant references to having fun, anything short of complete submission to the Tati audio-visual experience carries the risk of revealing oneself to be one of the square, too-serious types that Tati constantly teased
Images Journal calls him
one of the great comic icons of French cinema, a Gallic equivalent of Charlie Chaplin or Buster Keaton, whose works as director, writer, and actor are regarded fondly by audiences as well as harder-to-please critics.
Films de France says he is
that rarest of phenomenon in filmmaking – an auteur with extraordinary powers of observation and an equally impressive ability to entertain.
My blog post on Play Time (1967 France/1973 U.S.) is here.
Jour de fête (1949):
(in French, no English subtitles)