I don't think I've ever watched a weak performance from Andrea Riseborough. Quite the opposite. No matter the film, no matter how big or small a role, she's always on point with good or great delivery. Here she is given more room to stretch her acting skills since she's the titular character and ultimately it's the main reason to watch this. Having said that, there's a lot to like here besides Ms. Riseborough. The story of an alcoholic down in the slumps is not particularly original, but it's executed well under a solid direction. Apart from a couple of instances in the second half when it gets a little too easy and sappy, for the most part, there's a genuine vibe coming from the story and the characters (Allison Janney is another welcome addition to the cast) that I really appreciated, including some great scenes and lines.
Some minor flaws, among them, hint at things that never are revealed or come to fruition, or perhaps I read too much into it, but overall it's a good drama and another win for Riseborough, which gets this an extra half a star.