What are some strong literary aspects of "Casualty" by Seamus Heaney?

The first stanza of Heaney's poem is rife with compound words, or two words joined by a hyphen to create a new word. The subject of the poem is a "sure-footed," "dole-kept breadwinner" who puts on a "discreet dumb-show" to order a drink. Why does the poet choose these compounds in place of preexisting terms? It achieves two purposes. Firstly, it helps convey the compact, opaque, and even somewhat mysterious character of the subject. The man in question possesses a "deadpan sidling tact," he condenses his words and gestures only to what is necessary. Heaney does the same with these compound words. It also conveys that, while a weathered old laborer in a bar is a familiar figure, this particular man has a unique quality. Otherwise, the poem would not have to use unique terms to portray him.
Heaney's approach to rhyme in "Casualty" is also rather unique. Rather than a set rhyme scheme, Heaney wrote the poem in free verse, or without regular, consistent rhyme and meter. However, in this free verse, the poem does feature several examples of rhyme and slant rhyme. In part III, the poem depicts "quiet walkers / And sideways talkers" at the subject's funeral. The examples of slant rhyme include the instance in which "Everyone held / His breath and trembled." "Held" and "trembled" feel as if they could almost rhyme, but they do not.
The poet chooses to weave in and out of slant rhyme, regular rhyme, and no rhyme at all because it emphasizes the upheaval taking place in the poem's setting. It is a time of fear, chaos, and death. While some parts of life continue normally, and death itself even becomes normalized, things are never quite right. While some parts of the poem rhyme predictably, others take a jarring turn away from the rhyme scheme. 
The poem also features conflicting, unsettling imagery to achieve this same effect. Light and darkness never represent anything as simple as just pure "good" or "bad" in this poem. On the day of the subject's funeral, the "cold sunshine" faces off against "the land / Banked under fog." While the subject himself was drawn "towards the lure / Of warm lit-up places," it was light which signified his demise:

I see him as he turned   
In that bombed offending place,   
Remorse fused with terror   
In his still knowable face,   
His cornered outfaced stare   
Blinding in the flash.   

Lightness and darkness become conflated and contradictory images in this poem, which lends more gravity towards the overall feeling of confusion, dread, and upheaval.