So there's good news and bad news.
The good news is that Return of the Crimson Guard by Ian C. Esslemont is one of the best war novels, regardless of "genre," that I have ever read. The bad news is that it does wear genre trappings that may be offputting to anyone who doesn't appreciate or can't set aside those trappings.
Let's push through the bad news first. Crimson Guard is the second book in an ongoing series that is tightly tied to another ongoing series that is up to nine books. So a mainstream reader might feel compelled to read up to ten books before Crimson Guard, but it really isn't necessary. As I've written about some of the other books in the Malazan universe, the books are only loosely conjoined. In fact, despite a cast of dozens, as best I can tell there are only two characters in Crimson Guard who appear in any other books, and their role in the shared universe is fully explained within the pages of Crimson Guard itself. Therefore, the same sense of disjunction a brand new reader feels as they are thrown into a new world with new characters is similarly felt by an ongoing reader—most of what they are reading is new also.
The other genre issue that could be offputting is that the Malazan sequence is medieval high fantasy; in other words, the war that is fought in the pages of Crimson Guard involves soldiers in armor with swords, bows, and spears, and most disconcerting, sorcery. To some readers, the story being set in another place and time (and to be honest, with other races) delegitimizes the foundation of the story itself, despite the power and strength of its other elements. That's unfortunate, since there is still merit in reading, for example, The Red Badge of Courage, a fairly accurate depiction of life on the front lines during the Civil War. And I'm not saying that Crimson Guard is as important or as well written as Red Badge, but making the point that the kind of war should not taint the artfulness and the storytelling contained in a novel.
Return of the Crimson Guard takes place in three parts, a tightly built narrative structure—part one is the gathering of the armies and the individuals who offer the narrative viewpoints, part two is day one of the war, and part three is day two of the war. There is also an epilogue that tries to tie up some loose ends but mostly acts as a denouement to the final climactic scenes of the war that has just taken place. Esslemont artfully uses part one to develop a rapport between the reader and the various actors in the war while putting the players in position. The characters are uniformly fascinating, built as they are not just on exposition but in character interaction, even the ones the reader might find to be despicable. Again, it could be easy to get lost in place names without previous reference, but it doesn't really matter. Since the war that Crimson Guard describes involves armies with conflicted loyalties, the places aren't really important. What's important is the universal message of all war novels, that the armies are made up of individuals, not faceless machines—and those individuals have stories and lives. And because the war involves sides made up of former allies, a touch of regret and irony colors the events that take place in Crimson Guard.
To his credit, and to the book's strength, when war does arrive, Esslemont doesn't pull his punches. War is not pretty and survival is often a matter as much of luck as it is of rigor and skill. Characters that Esslemont has built up in part one die, sometimes horrifically, sometimes comically, in parts two and three. And often, if a character does not die, they have painful epiphanies that are just as wrenching to the reader as the deaths that are described. Esslemont's structure also allows him to contrast specific horrors of war—that is, is it worse to kill up close and personal with swordplay and crashing groups of highly trained groups of men, or safely and from afar, when sorcery is used as a sort of medieval weapon of mass destruction. For tactical reasons, neither side of the war use their sorcerers in part two, and little time is spent discussing why this is a sound tactic. Instead, we file through narrative viewpoint after narrative viewpoint detailing what seems to be about the worst conditions one can imagine. And in part three, when the sorceries do start up (in what can easily be read as a metaphor for modern advanced remote fighting if one so chooses), the scenes are equally terrible but in a different way.
Reading Crimson Guard is an emotional investment, made to care as we do for the characters written for us, and then watching so many of them die in all the ways that war allows. Its strength lies in that investment we make, so that each death also kills a tiny part of the reader as well. Each terrible decision takes its emotional toll on its audience. I suppose it can be argued that a lot of what I have said here would be true of any war novel. However, I don't think I've ever felt as invested in the people in a story as much as I do for the characters of Crimson Guard. And I really can't think of praise any higher that I could offer to a writer of any genre.