I actually really enjoyed the movie because it is verry profound and there are some interpretations:
1st is the pursuit of perfection, which drives Nina in the end crazy and when she reaches it she dies. It is true that she is the perfect white swan, but she loses that in the end. She reaches for the total perfection of many things. So it basically critizises our society or economic, political system in which errors are not any more natural and you need to be perfect in many ways. So our system is not perfect at all as there are no perfect people ...
2nd is that it simply plays the ballet swan lake inside Nina, she herself is Odette who is not caught in a swan but in ballet and does not even try to break out with love but wants to run herself deeper into it ... She manages to seduce, meaning to love her teacher by adapting the techniques of her friend, the personification of Odile. The question here is, who is the Odile, the teacher or her friend ... This level of interpretation also reffers to the first one, as Nina doesn t realize that she s trapped and is focused by the idea of becoming perfect... she s happy with her swan life.
3rd is an explanation why there are so many dreams. The original swan lake ballet hasn't been sucessful at first, because some major parts of it were removed and the tricky parts just replaced. So a lot of changing has been done and didn t make the ballet better ... so what the director did is just mix them up to have a ultimate modern version of it, that s why the ending could also be just a dream. He played swan lake not as what Tchaikovski originally wanted it to be but rather what it became.
This explanation unfortunately doesn't apply to all of the dreams, because some are just there to show the development of Nina or the changing of her character.
In total what the film wants to show us is that we can try to reach for perfection in one term (nina being the perfect white swan) but shall never try to combine many ones. So try to be yourself and don't get obsessed by to many opposing things :-)