Overall, I really enjoyed this book - it struck me as similar in a lot of ways to "Stumbling on Happiness" by Daniel Gilbert, in that it tries to apply scientific (or "scientific") research to people's problems.
My only real gripe is that the author goes out of her way to target the book specifically to heterosexual married couples; while that's what most of the research focuses on, a lot of the lessons in the book should be applicable to unmarried couples (gay or straight) who live together, and while I think they could also gain from reading the book, the author presents the research in a way that's not unfriendly, but still may alienate these groups.
There is one chapter that focuses on research surrounding gay couples, but the author still goes out of her way to discuss how these studies apply to heterosexual married couples.
I think she does a good job overall of not being too stuck on conventional wisdom, and she does try to point out when there are notable exceptions to trends, but the book does rely on some research that I find a little annoying, like the evolutionary explanations for things. Women are more detail oriented because back when dinosaurs roamed the earth.... etc. etc.
There are some points where the book seems to contradict itself, or where the research sounds a little iffy. For example, she discusses how the language couples use to describe things like the way they met is a good predictor of their likelihood of divorce. That may be true, but I'm not sure it's so clear that it's a causal relationship - sure, maybe the language we use can indicate our true feelings in some cases, but maybe people who use more negative language are simply more likely to get divorced.
Overall, though, as someone who will soon join the ranks of the married, I found it a pretty helpful discussion of marriage, and a good review of the research that's out there.