In the grim dark future, there is only black comedy. The word grimdark is a portmanteau created created by 4chan to make fun of the opening crawl of Warhammer 40K's text i.e. "In the grim dark future there is only war." This is due to the fact Warhammer 40K was originally created as a parody setting of countless over-the-top dark science fiction elements blended together with what was, essentially, a really dark campaign of Warhammer. Which was, itself, a really dark campaign of Dungeons and Dragons.
Eventually, the rise of George R.R. Martin resulted in grimdark being primarily applied as a term to doorstopper "realistic" fantasy stories in the same vein. The connection to Warhammer 40K was de-emphasized and there were actually questions whether dark science fiction qualified as grimdark at all. I strongly disagree with that, part of the reason I created Lucifer's Star, and will now share one of my favorite series from the Warhammer 40K universe. I speak, of course, of Ciaphas Cain, HERO OF THE IMPERIUM!
The premise for the books is a Colonel Commissar Ciaphas Cain has recently died of natural causes and his occasional lover, Inquisitor Amberly Vail, has decided to assemble his deathbed "confession"/memoirs into historical documents for the Inquisition's archives. The fact we know Ciaphas Cain manages to survive to a ripe old age despite living in the ultimate hellish universe and die as a beloved hero should suck all tension from the book--but doesn't, because the whole point of the series is analyzing what it means to be the One Sane ManTM in a universe driven by blind fanaticism.
Ciaphas Cain, you see, died as a legendary war hero but believes himself to be a secret coward and fool who survived myriad encounters with Chaos, Orks, Tyranids, as well Tau (one of these is not like the others) due to an inappropriate desire not to get himself killed in the line of duty. To facilitate this heretical idea, he also has the idea of keeping his fellow soldiers alive to serve as human shields against the enemies trying to kill him. The fiend!
Much of the book is a deconstruction of typical ideas found in fantasy (light or dark) where zeal replaces good tactics as well as prudence. Death is always around Commissar Cain so he does his absolute best to be prepared before things go utterly poing shaped (as he's fond of saying) as they inevitably do. Despite this, this isn't a source of pride to the Commissar but an actual source of shame as the body count inevitably includes friends as well as loved ones but he manages to escape to another day.
Cain is ostensibly based on Harry Flashman, at least the George MacDonald Fraser version but actually reminds me a good deal more of the WW1 incarnation of Edmund Blackadder. He is, much like said character, trapped in a situation destined to kill him (or not in Cain's case) so all of his deeds are designed around surviving that inevitable fate. Also, his resigned jibes contrast against the blind stupidity of those around him.
I'm actually as fond of the supporting as I am of Cain himself. Colonel Kasteen is a wonderful supporting cast member, serving as Cain's platonic life partner. A wonderful snarky scarlet-haired soldier who would have made an excellent protagonist in her own series. I actually was disappointed the author didn't have them hook up despite that being the embodiment of cliche as well as against regulations. Note: Cain, amusingly, has a quite active love-life despite the fact his primary lover could have the planet he's on bombarded.
Cain's Valhallan unit from a Nordic-Russo Ice world is a dark and hilarious gang of killers who are more upset about the fact they have different dining habits than they're all going to die horrifyingly in their next engagement (probably). The fact it's made of two single-sex regiments smashed together is also a source of some intentional hilarity in the early parts of the series.
Fans of grimdark may think this isn't a qualifier because Commissar Cain is hilarious. His dry observations, wit, and ability to out-think his enemies aren't very grim. However, the world is still portrayed as a horror show of tyranny, fascism, and various monsters out to eat humanity at every time. The fact it's presented in a jokey off-hand fashion just makes it more fun like how "The Wheels on the Bus" now includes lines about running over heretics in kindergarten.
Weirdly, the enemies are also made more terrifying by this approach as the Orks go from being soccer hooligans and working class Londoners to being an implacable force of destruction. Similarly, the Necrons are a mindless unkillable army of Terminators than the somewhat pathetic slaves of their masters which gamers know them to be. Even the Tyranids show themselves to be clever and dangerous conquerors than "mere" animals.
The books are annotated, it should be noted, by Inquisitor Vail as she adds a near endless amount of funny details to the story. Commissar Cain is trying to be self-deprecating, after all, while she's more interested in the truth both good and bad. Cain is also a raging egomaniac even when trying not to be so he only talks about events which pertained to him and often misses the larger context--that the annotator corrects. It must have been murder on the Black Library editors to do the books this way but I think it's one of the series' best parts.
The first omnibus puts the protagonist against Tau, Tyranids, and Necrons in stories which I completely approve of. If you are a newcomer to Warhammer 40K or a long time fan, I recommend this collection. I note also recommending the collection since Black Library still refuses to release their books on Kindle so it's better to just get the larger volume than try to collect all the smaller ones.