I think I got the point of it...but I feel the style overcame the substance a little too much.
In other words, I don't feel that the three timeline structure was necessary for the film's message. The same story could have been told using only two, or perhaps even one timeline, and still have the same level of impact that the film has. This was my initial impression. It may change upon repeat viewings.
I don't think Aronofsky exploited the concept of the multiple timelines as best as he could have. The guy in the floating bubble was a shining example of over-indulgence - he didn't really do anything pertinent to the rest of the story. Others have said that it's too ambitious...but I actually feel the opposite. I don't think it was ambitious enough. I wish it integrated the different stories so that there was a deeper message or meaning to the events in each timeline so that a simple action in one had a relevance in the others, but that doesn't appear to be the case, with the possible exception of the climax.
I enjoyed it for what it was, but I can't help but see a better film that wasn't made in its place.