Laurie Metcalf is a very talented actress. She seems to portray neurotic, eccentric, psychotic, or perhaps any number of other "personality disorder" type persona's in very convincing ways.
It's her supporting roles and acting ability that gives a competitive edge to any show, film, or performance she appears in. I don't think enough can be said, and certainly feel that she is underrated in her category of professionalism.
Her supporting role character as Marcie Dahlgren-Frost in the movie "Uncle Buck" - http://www.youtube.com/watch?v=5VSjOzmW4_E was an exceptional portrayal of her uncanny gifted talent, further convincing that her acting can really brush both familiar and unfamiliar at the same time.