Ocean at the end of the Lane

I read an interesting book recently, The Ocean at the End of the Lane by Neil Gaiman. In Ocean the nameless adult protagonist returns home to Sussex for a funeral, wanders onto his old neighbors' property and recalls a childhood adventure. It's a beautifully-written engrossing, terrifying adventure to be sure.

For a fantasy, there are some delightful references to modern science such as wormholes, alternate dimensions, the Big Bang and the like. Neat! But ultimately for this reader it was a sad story, seeming almost autobiographical, even while describing mythical powerful creatures.

All in all, I'm not sure I got this book. The protagonist seems to be remembering his childhood to gain some secret power/weapon/knowledge but he immediately forgets. Moreover, the reader's told he has remembered and forgotten it before. Apparently the protagonist--and by extension all adults (?)--are doomed to ignorance and powerlessness. Or...?

What do you think this book is about?