How ironic that ''Far From Heaven,'' Todd Haynes' tribute to '50s weepies maestro Douglas Sirk, is reaping the kind of critical respect Sirk's films rarely got. They were generally dismissed as too over-the-top and campy to be worthy of serious consideration. Imitation of Life's ostensible stars are Lana Turner (lacquered and stiff) and helium-voiced Sandra Dee as an ambitious stage star and her neglected daughter, respectively. But it's Juanita Moore as Turner's African-American maid/confidante and Susan Kohner as Moore's tormented, light-skinned daughter who tries to pass for white who make the movie click. Sirk invests their tortured relationship with a visceral intensity that peaks in a quietly heartbreaking scene between the two in a Hollywood apartment. And though ''Imitation of Life'' is not Sirk's best (that would be ''Written on the Wind'' and the currently unavailable-on-DVD ''The Tarnished Angels''), it's still a prime example of a brilliant director's stealthy use of a denigrated genre to slip in subtle social comment and genuine pathos.