A few tidbits from "The Late Flowering of Geoffrey Hill" by David Gervais in PN Review 183, 35.1 (September-October 2008):
"...what gives Hill's verse its name for 'difficulty' is less its abstruseness (things can after all be looked up) than its refusal to spell out the links in its chain."
"...Hill's verse is not 'difficult' because it is recondite but because it puts us on the spot as readers, that is, on the spot both morally and aesthetically."
"The hostile voices that disrupt the surface of Speech! Speech! are ultimately inseparable from its 'noble vernacular', woven into the fabric of the very poetry they threaten. Nothing better shows why Hill is essentially a public poet than this obligation he feels to include such alien voices within his verse even when they run counter to its lyric inspiration."