Reading that before the poems themselves would go a long way to put a reader in the right frame of mind. Reading it last instead made this reader think he'd missed the whole point, and made him faintly annoyed by Heaney's editor.
Heaney is one of the declared great poets of the twentieth century - he won the Nobel, got extravagant praise his entire career, and was a noted Harvard professor for a couple of decades. He also grew up in Northern Ireland and lived through the worst of the "Troubles" - though, reading between the lines, it seems that he moved to Dublin pretty young and America in his early thirties, so his view of NI, for most of his life, was that of an expatriate.
That feels appropriate to me. I may be cynical, but Heaney's matter feels very "auld sod" to me: mythologizing, backwards-looking, celebrating things he has personally left behind and wants to engage with only on the level of his tightly-controlled writing.
I have to admit I struggled through a lot of Opened Ground. I found it full of far-too-precious, far-too-specific Irish farming terms, words with immediate meanings only to people of Heaney's generation and heritage or older. Specificity in poetry is a good thing: I'll never deny that. But it has to be specific in ways a reader can get into, and I found Heaney's word were barriers to meaning: for me, maybe for Americans or people of my generation in general.
Halfway through, I formed a cynical schema. Heaney's poems, I postulated, were all metaphors. About half were metaphors of a rural scene of his youth: a village blacksmith, a horse pulling a plow, the color of sunlight on a Tuesday morning in June through one particular tree. The other half were metaphors for Catholicism. Eventually, I decided that was too limiting. Instead, every single Heaney poem was both: it used Irish rural dialect words about random farming details as a metaphor for Catholicism. And sometimes for the Catholic-Protestant sectarian battles, in which Heaney would not officially pick a side (even though the Irish Catholics, the greatest people on earth, are clearly correct and clearly horribly downtrodden).
Heaney wrote about people as types, not persons. He almost never uses names, instead starting with pronouns - almost exclusively "him;" women are mostly absent in Heaney's poetry other than glancing references to the fecundity of his mother and wife - and commonly writing from the viewpoint of himself as a very young child, bedazzled by the worlds of manly work and honest toil.
The Nobel lecture talks about his reasons for this - why his work is so intensely about his viewpoint, about being Seamus Heaney at its core, this person born into a troubled land at a troubled time, and trying to write about it in ways that won't get him stood up by the side of the road and shot the next time he comes back to visit family. I appreciate all of that. I appreciated it once I read the lecture, and would have greatly appreciated having that perspective before reading the poems.
There were lines I enjoyed greatly, probably even a few entire poems. I found a lot of it too precious, in that so-common poet's way of being besotted with glittering, quirky words. I expect readers who did grow up in a rural district, or in Ireland (or possibly the British Isles in general) will find many more of those words more homey and immediate than I did. My favorite bits of Heaney were his translations: he worked quite a lot from the ancient Greek, perhaps seeing an echo of the conflicts of his own life in the Trojan War. (I did also read his translation of Beowulf a long long time ago - that may have been the reason I got this book in the first place, way back when.)
I usually end my post about books of poetry by exhorting whoever is reading to read more poetry. I'll do that again here, though it probably sounds like faint praise, since I didn't click with Heaney the way I'd hoped. Still, poetry is clarified, intense, distilled language. If you read, you need to tackle the hard stuff now and then. Maybe not Heaney, unless you're either quite different from me or ready to read the afterword first, or both.