It's nothing you'd expect from a Punisher story. There's a framing story, but most of the book's from 1960, when he was ten years old. This innocent young Frank Castle kills no-one, commits no violence and indeed doesn't really do much. He likes poetry. The art's soft and gentle, like book illustrations. The shooting of some gangsters in the framing story at the end is silent, almost beautiful, on a snowy evening.
"They'll blame it all on Vietnam. And they'll be right. And they'll be wrong."
In 1960, what really happens only comes to Frank (and us) second hand. He doesn't see what's going on directly. He doesn't understand it. He's clever for his age, yes, but he's not ready for rape and suicide. This is a poetic story, with the title being a William Blake reference. (Those famous lines resonate with our anti-hero, in a rejection of simple reasons to "explain" why he became the Punisher. Yes, he lost his family. Yes, he saw horror in Vietnam. That's all true, but here we see that darkness fascinated him even when he was innocent and meek.)
It's also a study of the historical period. What you did and didn't say in the 1950s. What that covered up.
Is this story exciting? Definitely not. Is it horrible? Yes, but mostly in the cracks between the pages, in events that happened offscreen. (Even the framing story's traditionally gangster-killing Punisher is young and fresh-faced, incidentally. In his own way, he looks innocent too.) I wouldn't call this story a favourite, but it's fascinating for being so unlike everything else Ennis did with the character.