The structure of the film is very straight forward, quite possibly it was chosen not to get too experimental, maybe to not to confuse the audience any further. Sure, Arronofsky was afraid of another Gitai moment with Portman - so would I have been. But the story becomes predictable at one point and I've felt that when the bifurcation of the personalities was over the rest was only dance scene - no more story or character development.
Maybe Cassel's character could have been a bit heightened and made even more brutal in his egoistic strive for "his" perfect dance company. On the other side maybe Ryder could have been de-splattered a bit, her psychology is also quite interesting.
Great cinematography and the vfx stayed happily in the background to do a great job. Interesting is the grainy look of the picture giving it a "homely" feeling.