Before I get into the time travel aspects of the film, let's look at why the relationship didn't work. It's my understanding that the book the movie is based on is a tremendous read and really delivers on the emotional moments. In the movie, however, I think the writers/director did a very poor job of making me understand why these two people love each other enough to put up with the crap they have to go through to stay together.
For instance, Rachel McAdams's character shows up when the time traveler, played by Eric Bana, is a down on his luck twenty-something. All it takes is for McAdams's character to say that she loves him and knows everything about him and Bana kind of just shrugs his shoulders and thinks to himself, hey, she's kind of good looking, I guess I should love her now.
Then there is the whole fact that the girl's love for the time traveler is based off of her childhood infatuation with an older man. It just felt wrong to me. Her love is entirely plausible but just icky. It was like I was watching the time travel version of the Celine Dion story.
Thinking about my confusion with the time travel in the story, I believe a lot of my over thinking could have been solved with a better visualization of Eric Bana. He always looked the same to me. One second he has a beard and the next he doesn't. The make-up department's grand illusion to make him look older was to give him facial hair. Well, he has face scrubble when we first meet him in his twenties so the whole time I'm trying to figure out which version of him I'm looking at instead of getting emotionally invested in the story.
I've been picking apart the movie up to this point. I suppose it's my frustration with a film I generally liked and feel that if they had done better with the points I mention above I would have really liked the movie.
The actors do a good job with what they have to work with and if you buy the reasons for them being together you start to see the chemistry between the actors. I also thought the last one-third was quite poignant and really well done. I just wish the set-up was as strong as the finish.