Wild at Heart is a book written to encourage men to reconnect with their masculinity and to take joy in their identity as men. Eldredge's thesis is that men long for essentially three things: a battle to fight, and adventure to live, and a beauty to rescue.
I found Wild at Heart to be encouraging to a certain degree. Society in general derides masculinity and either caricatures it in super-macho bravado or neuters it in pressing men to be passive and mediocre. I myself often fail to step up as a man and take initiative in situations requiring leadership. In this context, then, the challenge to live out my manhood with passion and energy, willing to take risk and put myself on the line in order to pursue the challenges that God has given me is presented effectively and forcefully.
I do have some concerns, however. When speaking of the need to be a risk-taker, Eldredge points out God as our example. Although he says that he is not entering the "open theology" debate, saying that God takes risks implies that even for God the future is uncertain. The application (that we men need to be risk-takers) is good, but the theology to get there is bad.
My other, less specific concern is with the book's Scriptural underpinnings in general. Verses are cited here and there, but the main idea seems to be supported at least as much by introspective intuition and cultural references as by the word of God. These elements are helpful in drawing things out that we see within ourselves, yet I would still have liked to see the book stick closer to the Biblical text.
Overall I would say the book was helpful, but I would like to find another book on this issue that handles Scripture more carefully and is more theologically sound.