In a nutshell - it's excellent, and well worth a read. This is a long review, but I'll sum up here first:
Engaging, fascinating read that covers the broad spectrum of both human strength and human suffering. A story about a man whose life has been a quest for personal strength, strength he found by committing to helping those in need.
Throughout, however, no matter who is being helped, no matter what conflict is being described, the overall tone of the book is one of someone with a driving need to *do.* For others, yes, and to help - but first and foremost for himself. To satisfy a hunger to be more than he is.
Long review follows-

Having read through it in two days, this book isn't what I expected. I expected a Karate Kid story about a wimpy nerd/humanitarian who is pressed so hard by the injustices of the world that he becomes a warrior. I find those stories inspiring, when people are given strength by a cause.
This book, by contrast, is about a hero without a cause. He already was strong, his first act detailed in this book is becoming a junior golden-gloves boxing champion, hardly the wimpy beginning I imagined.

That said, it's more than I imagined as well. A story about a traveling humanitarian, who goes to country after country across the world to help starving children, embattled refugees, the sick and the poor. But in each place, over and over again he hears the people he's helping say "Thank you for helping - but why weren't you here sooner? Why didn't you stop this from happening in the first place?"

And that's why he joined the Seals. Which is a course of action that makes absolute sense in his life.
Much of the book is spent describing his (Eric's) training, whether that be for military special ops or boxing teams or karate. The focus of the story is the internal, personal growth of the author. I found this compelling myself, but it does detract somewhat from the others' in the book, even those who months or years of the author's life were dedicated to helping. I found them to be flat, arguably somewhat two-dimensional in the book. I couldn't help but see some amount of self-fascination in the writing in the book, but that doesn't make it any less worth reading.
Parts such as descriptions of what's being done to actually make progress in Afghanistan and Iraq especially I found fascinating. The new focus on working with the local authorities and concerns, rather than despite them, is something Eric emphasizes in several places in his journey. Something that isn't being done enough and has great potential for reducing conflict.

The things that stood out most for me where the moral questions, especially those posed by refugees - and of those most especially the ones in Eastern Europe. Most of those questions circled around the confusion over why so much help was available only after atrocities were committed, not before. Why is international aid so easy to get, while protection is so hard? Why do people contribute so much to ease suffering, but so little to prevent it?
That's the central question of the book, and one Eric answers by claiming (rightly, I think) that there is desperate need for the Fist (warriors and protectors) to protect the hearts (humanitarians and refugees) of the world.