Oh, wow, I'd love to have seen Nixon play the part. I loved loved LOVED Mary Louise; she's one of my favorite actresses. I think she's brilliant, though much more powerful on stage than she is on screen.
There are a lot of people who didn't like her portrayal of Harper, though. I think some people sort of feel like she went way overboard with the drug addict thing, and all of her monotony was annoying. Which... I can see where that would come from, but I don't agree. Love her.
A work of art is an invitation to love.