In between the first 20 and last 20 minutes this is an excellent film. Absolutely top notch dialogue -- smart, biting, and very well delivered. The plot is layered nicely and introduces several interesting meaty characters. Unfortunately, because there are so many, we don't quite get to the depth of any character. Still, it's a nice ride with quick to the point interactions that make for a great pace. I really liked the middle of this picture.
The first 20 also deserve praise for production value, but simply as a matter of taste -- I found it quite hard to watch one nasty personality take advantage of an open-hearted one. Thankfully, the film isn't all about that kind of abuse; however, it's simply necessary to set up what the film is really about.
As for the last 20, things move too quickly for plausibility with regard to one relationship. And the film chooses to end on that in a rather cliche way. I would venture to guess such an ending wasn't the intention of the original writer. The film's dialogue is so good, I'd expected it to hit a home run with a very heartfelt ending, but instead ends a bit soft.
My suggestions: open the film with shots of the sisters as little girls, warming us up to the love between them. That connection remains missing the whole film. Towards the end, we hear in words some support for that love, but it's too little too late.
Still, I enjoyed the piece -- very nice middle, sweetly directed, acted and edited.