While it's likely true that few current critics rank it with the best Williams, I'm not sure that no critics rank it with his best. And perhaps if they saw good productions of the play more often, they might.
From reviews of the 1966 City Center revival, which moved to the Billy Rose (and was happily preserved in a wonderful Caedmon recording):
"I suspect that critics—and, more important, audiences—of the future are going to be as taken with this play as with anything in the Williams canon." — Dan Sullivan, New York Times
"The play stands in the first rank of Williams' work, perfectly balancing his poetic vision with rough, slam-bang humor and spine-tingling vitality." — Cecil Smith, Los Angeles Times
"One of Tennessee Williams' most appealing works, since it stresses comedy that comes from native behavior." — Ethel Colby, Journal of Commerce
"A classic among modern American plays." — Norman Nadel, World Journal Tribune