If you've seen the commericals you know the film takes place in three different time periods. Tying together the past and present seemed to work successfully, largely because it was left to the viewer to determine if, in fact, Izie and Tommy were these same two individuals or they put themselves in the context of the story that Izie was writing. The neat thing is it works either way. It's the scenes set in the future that leave the viewer scratching their head. Some of it works if we believe it's Tommy and he's found a way to extend life far, far into the future. Stories and myths Izie told him in the present come into play and I like watching plot points come together. But even if we buy that Tommy lived hundreds of years beyond what is now a normal life span there is no way the human race is using bubbles to transport themselves through space. And the kicker is that Darren Aronofsky didn't have to even go to such far out means to get his point across, because the 'moral' of the story is something that deep down we all know already.
Still, if you are a Hugh Jackman fan as I am or like seeing really good performances or stunning visuals or like being made to think than I would recommend seeing this film. But be prepared to handwave and roll your eyes in some spots. Oh, and did I mention Hugh half dressed, wet, and in a tub with Rachel? ;-)