There's not much to recommend this movie. There's no real chemistry between Ben Affleck and Gwyneth Paltrow, which is a shame because they're both talented actors, and they've both proven they can do romance. They just don't do it here. In fact, there's so little connection it's obvious they're just reading scripted lines. In the end, it's neither their fault, nor the writers: the lines are all right, and they're read well, but there's just no chemistry.
There are only two major failures with this movie, but they're doozies: the characters and the plot concept. The characters fail to grow on viewers despite all the standard awkward situations they're put into to create sympathy. Affleck's guilt over Paltrow's husband seems contrived, rather than genuine or understandable. He is a sterotypical villain, ready, even eager, to prey on others. Even his career is sterotypical: he an ad exec; of course he's a horrible human being. His character fails: a flat-character bad guy that almost, but not quite, becomes a likeable guy. His guilt and self-loathing seem contrived. Paltrow's character fails as well: you sometimes feel sorry for her, but never really sympathize.
The other major failure is the plot twist. The only redeeming factor is the that-could-have-been-me factor, which is given away in the trailers and not developed in the movie. If they had spent more time developing his character around that, and not forcing him to persue Paltrow's character, this movie might have been saved. Instead, they use it as a cheap plot device, and throw it away.
There's not even anything to qualify it as a decent chick-flick- there's nothing to sigh about at the end, you never say "just say yes, you twit! Can't you see he loves you?". It's a little too much like watching a very boring episode of Springer, minus any redeeming drama.