The poetry here is of a more post-modern cerebral variety, not so much providing emotional oomph, but rather more of an intellectually isn't that neat. Absence, what is unsaid, blankness, erasure, as the title implies is as important as the visible words on the page. Many of Henry's poems drift across the page in jagged lines, leaving visual white space abounds, while many other poems have words and phrases blacked out, omitted, and still others feature lines crossed out by still visible. What is said, what isn't said? What's more important?
I'm not sure there's an answer, and Henry doesn't give you one, purposefully not connecting the dots, but rather colliding phrases in ways that makes you sure something is missing and then leaves it to the reader to determine if and what it is.
I think this kind of poetry is perfectly fine, and I'm certain there are a number of readers who would be jazzed by the intellectual spirals this kind of work could create, however, it doesn't resonate for me on anything more than a "that's neat" level. I read through the book fairly quickly, and with the exception of one or two poems, found not much that lingered after I put the book down -- another form of "lessness", I suppose.