The soldiers are obviously under a great deal of strain when they are on the line. The following quote expresses the idea that in battle they are animals, but away from it they change entirely in order to cope. "Just as we turn into animals when we go up to the line, because that is the only thing which brings us through safely, so we turn into wags and loafers when we are resting. We can do nothing else, it is a sheer necessity." This gets at the idea the war changes people. They can't maintain their intensity when they have a chance to relax, and they can't relax or maintain their humanity when the have to fight.
An excellent place to look for style and metaphor information is right here on eNotes: the study guide for this work is comprehensive but lacks a specific quotation page.
This blog post has some interesting quotes.
Here is a powerful quote regarding the mindset of a soldier during wartime, comparing the ground to a nurturing and always forgiving mother-figure:
To no man does the earth mean so much as to the soldier. When he presses himself down upon her long and powerfully, when he buries his face and his limbs deep in her from the fear of death by shell-fire, then she is his only friend, his brother, his mother; he stifles his terror and his cries in her silence and security; she shelters him and gives him a new lease of ten seconds of life, receives him again and often for ever.
The most powerful language in the book, in my opinion, is reserved for comments on the effect the war had on Paul's generation:
I am young, I am twenty years old; yet I know nothing of life but despair, death, fear, and fatuous superficiality cast over an abyss of sorrow. I see how peoples are set against one another, and in silence, unknowingly, foolishly, obediently, innocently slay one another.
A wonderful example of a metaphor is Paul's comparison of the front to a whirlpool:
To me the front is a mysterious whirlpool. Though I am in still water far away from its centre, I feel the whirl of the vortex sucking me slowly, irresistibly, inescapably into itself.
I would suggest the opening and closing sensory images. The bitter irony they produce, despite the narrator's calm, quiet, distanced tone, is bitingly painful and thus perfectly representative of the spirit of the narrative;
We are satisfied and at peace. [...] I am very quiet. Let the months and years come, they can take nothing from me, they can take nothing more.
The power of these images,especially when juxtaposed, is confirmed in the Dedication of the novel:
This book is neither an accusation nor a confession, and least of all an adventure, for death is not an adventure to those who stand face to face with it. It will try simply to tell of a generation of men who, even though they may have escaped shells, were destroyed by the war.
Here's a memorable passage from the book. In this case, the tone is not grim but happy. The narrator and a friend have brought parts of a cooked goose to share with some comrades:
Kropp and Tjaden take us for magicians. Then they get busy with their teeth. Tjaden holds a wing in his mouth with both hands like a mouth-organ, and gnaws. He drinks the gravy from the pot and smacks his lips: "May I never forget you!" We go to our hut. Again there is the lofty sky with the stars and the oncoming dawn, and I pass beneath it, a soldier with big boots and a full belly, a little soldier in the early morning--but by my side, stooping and angular, goes Kat, my comrade.
This passage is quite sensuous, but not in the expected ways. It contains a very memorable simile in the reference to the mouth-organ. The verbs are vivid. Alliteration is effectively used, as is balanced phrasing ("with big boots and a full belly"). There is nice variation in sentence length (the very short "We go to our hut" is followed by an extremely lengthy sentence). All in all, this is a well-written passage in numerous ways.
For me, one of the most significant passages of this book which contains some very important words and phrases comes when the narrator begs forgiveness from the soldier he has just killed:
Why do they never tell us that you are poor devils like us, that your mothers are just as anxious as ours, and that we have the same fear of death, and the same dying and the same agony—Forgive me, comrade; how could you be my enemy?
Key to note is the use of the word "comrade," as the narrator claims a kinship with the enemy soldier that exposes the falsity and horror of war. Also note the repetition of the words "the same," and "poor devils" to help strengthen the idea presented by the narrator that there really is no difference between soldiers, which ever side you are on.
Great imagery and some humor:
Half and hour later every man had his mess-tin and we gathered at the cook-house which smelt greasy and nourishing.
A wonderful simile:
He sits down to eat as thin as a grasshopper and gets up as big as a bug in the family way.
...Stanislaus Katczinsky, the leader of our group, shrewd, cunning, and hard-bitten, forty years of age, with a face of the soil, blue eyes, bent shoulders, and a remarkable nose for dirty weather, good food, and soft jobs.
I would suggest the following descriptive words/phrases from the novel: shrewd, hard-bitten, with a face of the soil, intimate flavour, pithily, Iron Youth, as if moved by a vision, mysterious whirlpool, and barrage.
I would suggest visceral, gloomy, surreal, and symbolic. There are a lot of passages that are very descriptive. Since it is a book that is not afraid to describe the realities of war, there are going to many dark elements, but what has always struck me are the passages about trying to return home.