I first read this book a dozen years ago (at about age 30), have a thoroughly marked-up and re-read copy, and can say that it articulated so many obvious truths about male-female dynamics which weren't part of the general cultural discussion then (or now) that it was the sort of total revelation that other reviewers write about here much more eloquently than I can. I had previously believed that I was light-years away from being the typical male (choose your term: jerk, loser, etc.), but gained valuable insights from the book into how the typical female regards men and why my inner qualities were irrelevant or seemed to work opposite to the way I'd expected based on listening to what women say -- which solved a major puzzle. The strength of this book is that it's based on observations of everday behavior and what people do, rather than what they say.
While many of the examples (Michael Jackson, the movie Flashdance, etc.) are a bit dated at this point, Farrell's observations were years ahead of even the radical evolutionary psychologists in coming around to the view that men, and male behavior generally, are basically the result of a breeding experiment run by women, not men. This is a liberating data-point for men, who have been alternately shamed, chided, and pitied by women unrelentingly for about two decades now.
While much of the men's movement has progressed to more of a focus on political issues (divorce and child custody in particular), and Farrell's subsequent "The Myth of Male Power" is a stronger refutation of the widespread allegations of rampant male privilege (read it next), "Why Men Are The Way They Are" is still about the best book written from a male-friendly perspective on courtship and basic relationship issues, exploding many myths about men and women, which can only be a good thing.