Short form: I really liked this book, and intend to recommend it to a lot of people, and will probably just unilaterally buy it for some of them as a gift.
Executive summary: Levine and Heller take the basic ideas of attachment from Bowlby/Ainsworth and translate them from the mother/baby dyad to the adult romantic dyad. They assert that individuals have attachment styles (most are "secure", and the remainder are largely split between anxious and avoidant), altho they do recognize that these styles can change over the life arc. In an effort to get more people into secure attachment relationships, they encourage anxious attachment types to avoid avoidants, and date secures instead. They provide quizzes to identify which type you are, profiles of each type's behavior while dating and tips on how to move yourself in the direction of _being_ secure in addition to dating secure.
Needless to say, I have some Issues (boy, don't I always). While Levine and Heller are prepared to recognize that there are compatibility issues other than attachment style, they spend a limited amount of time on them. The good news is that they are seriously prepared to encourage people to exit a relationship and they even offer some astoundingly useful advice on how to do so successfully. This is mind-bendingly better than pretty much any other couples therapy out there. And I believe Levine and Heller are correct to identify being-in-a-relationship-with-an-avoidant as the Biggest Problem, and therefore the first one to resolve. I also think they are correct in observing that you are way more likely to run into avoidants while dating vs. their representation in the overall population (oh, look: an organized way of thinking about professional daters!!!).
On the one hand, I feel like there might be a certain amount of kicking the emotionally disabled by putting so much blame on avoidants. On the other hand, this crowd does wreak a disproportionate amount of havoc and is singularly uninterested in getting/giving help. And the analysis is incredibly satisfying, in that if universalized in the Kantian sense (if all secures and anxious attachment types refused to date avoidants), it would be poetically just (avoidants would all be stuck with each other. Serves Them Right. See how _they_ like it.).
If you do read it (and I recommend that you do), pay close attention to the details. They are useful details. Because the book is a fast read, it would be pretty easy to turn the content into a less useful cartoon of itself. I'm going to read the most recent Sue Johnson covering approximately the same material, and then contemplate rereading them both.
While this is a different approach than Gottman's, the two are largely compatible. If you are careful to avoid involving yourself with (or being!) an avoidant, the advice from Gottman should actually work really well.
ETA: Also, Levine and Heller are quite adamant about the hows and whys of effective (viz. direct, unambiguous) communication as part of establishing and maintaining a secure attachment, whether that's your "natural" type or note.
Bartholomew's language is a little different. "Fearful" = anxious-avoidant, "Preoccupied" = anxious, "Dismissing" = Avoidant
Bartholomew's final paragraph is worth paying attention to:
"The four-category model conceptualizes working models that are more or less consciously held, though they tend to operate automatically. We presume that at some unconscious level prototypical dismissing individuals do feel negatively about themselves, and their adoption of a detached stance toward others is a way of defending a fragile sense of self from potential hurt by others. Similarly, the positive other-model of the preoccupied masks a less conscious negative model of others, with the tendency to idealize others acting as a defense against acknowledging that significant others are, at least at times, uncaring and unavailable."
And this is why I feel bad kicking the avoidants. Even tho they sort of deserve it.