Maureen Stapleton is one of those actresses that can impress even in junk, like her role in THE FAN. The movie is barely better than a slasher film (despite the big stars), but Stapleton is magnetic.
I think she's at her best in INTERIORS, but as bk said, I can't remember a bad performance from her.
I loved what she did in the first episode of PLAZA SUITE, but I would also like to have seen her in the other two playlets, especially the last one (repeating her Broadway roles).