There is always a certain amount of expectation on any film made from a very popular book, and The Time Traveler's Wife certainly was that. Selling millions of copies (as well as the film rights even before the book had been released), this story of a time traveller called Henry and the effect his ability has on his wife Clare is obviously something with a lot of appeal right off the bat. Casting Eric Bana and Rachel McAdams in the respective roles was a shrewd move as Bana is such a fine actor and McAdams probably the most chameleonic actress in her age group. Both the central performances are fine and at all times watchable, but neither of these talented people are being stretched very much dramatically at all and that is a shame. They aren't asked to give too much of themselves because what they are giving themselves to is so consistently being distilled down to the bare minimum.
Firstly, given that this is a film which is ostensibly (and has been marketed as) first and foremost a romance, the psychology and bedrock of the couple's relationship is extremely questionable. She loves him because he's been visiting her since she's a little girl and is her "best friend" yet they get together by him meeting this random woman who professes to love him and he has sex with her pretty much on sight. Now this is not to say that the average male wouldn't do that when faced with the proposition of Miss McAdams being so obviously available, but romantic it hardly is. This is then accentuated because the filmmakers do not get into the basic fundamentals of the relationship. They can't focus on McAdams' character too much because then you'd just have a movie about a guy in his 40s grooming an 8 year old girl which would make it weirder than it already is, and they don't flesh out at all if or why Bana has any strong feeling for her. When he proposes to her he does so saying how he doesn't feel alone any more, but when they haven't explored that aspect of his character before, it leaves the moment flat.

This is sadly a theme for most of the film and that is also down to the structure of the narrative. By flitting between his and McAdams' perspectives and having her tell him things he will later come back and do, and seeing him actually come back and do things, whilst basically running forward in real time, it divorces these moments from their emotional aftermaths. This means that for the most part you see her experience something with him being from the future, but then don't see what it means to him as we normally don't then go to him getting back and seeing where it fits in with his emotional state. An example of this is their wedding day, shortly before they get married he time travels somewhere, then another Henry from the future steps in and experiences the moment, but we never see what finally getting to do that meant to him or how they as a couple then finally had that "shared" moment when his experiences catch up to hers. There are exceptions to this (for example on their wedding night we see him come back from seeing her as a child), but this just highlights the uneven approach to the storytelling and prevents a lot of moments from taking hold as they are not shown in their proper context, whereas others are.
What all of these problems show is not that this is a bad film, far from it, but the ways in which it is not as good as it could have been. The end is emblematic of this as it just isn't as emotionally hitting as it probably should be on paper and that is down to the consistent lack of depth in the way the relationship has been initially drawn and shown throughout. Apparantly there is a different ending in the book which surely would have more of a payoff, but as American test audiences couldn't recognise McAdams in age make up it was ditched and the film delayed for a year as a result trying to patch up a different ending. This missing of what is important is seemingly central to the direction, writing and production of the film. In a film like this, the romantic relationship is paramount and the filmmakers cut it off at the knees as much as they humanly can (even suggesting at one point neither of them ever had any choice in getting together and they'd be better off apart). The film looks nice, there's a lovely score, the acting is fine and it's very watchable for long stretches, but the sense of loss, of chances missed, of potential unfulfilled permeates throughout this intriguing, yet misfiring film.
I completely agree, pretty much word for word. I really could just feel the potential dripping from every pore of its body, but they turned it into such schlocky stuff.