I've seen that in a lot of the criticism about the movie, that it's pretentious. What parts were pretentious?
I found the story to not be concrete enough. I'm a writer, so trust me - I appreciate ambiguity. However, I think the film sometimes veered so far into ambiguous territory that it lost focus. That was the weakest element of the film to me, like Aronofsky didn't have the raw skill to capture this huge vision he had, and then got lost in his idea.
For all the film's ideas and visual flair, it still needs to tell a story. Which it does, but not as well as it could.