The plot can effectively be summarized in a single sentence: a group of women attempt to escape the asylum where they've be institutionalized. When you get to the psychological aspects of the film, they're attempting to escape reality. The metaphor of a burlesque/brothel is not too far from the reality they are stuck in. When they attempt to obtain the items they need to escape, they view it as a mission, as a fight for survival. But, eventually, reality comes crashing back down on them and the audience.
I must admit, I'm not entirely certain I liked it. I thought it was a well thought out film, well written, and incredibly visualized, using symbolism on top of metaphor to try to describe what the girls are going through, both emotionally and physically. But I must admit, the film did ultimately leave me feeling really uncomfortable, despite the denouement trying to let the audience know that everything worked out, villains were punished and heroes succeed, etc.
I don't know if it was the concept of the exploitation the girls were going through, or the sucker-punch twist, and even though I'm glad I watched it, I don't know if I'd see it again.