The Ciaphas Cain series of Warhammer 40k are formulaic - Cain is landed in a conflict with faction X, he connives, swears, and sometimes fights that faction, but the reality is, the conflict is a blind, and there is something else lurking behind the scenes, ready to ruin everyone's day. This does not mean they are bad books - if anything, they're quite fun, a bit of literary comfort food. However, it does mean that you should not binge them, as the average reader is likely to get bored of the formula rather quickly. Someone probably should have mentioned that to the Black Library folks at GW, since I imagine the omnibuses get hit with a lot of flack as a result.
In any case, all of the Cain stories are written as memoirs of a self-loathing hero, who is convinced he is nothing more than a craven coward. However, the careful reader notes that the man protests too much, probably driven to deny his actual bravery and compassion for his comrades by the Imperium's culture of post-apocalyptic martyrdom. Anyway, Cain is cynical and sardonic, ready to dispense quips at anyone's expense (including his own), and the footnotes (written in-universe by his love interest Amberley Vail) take all the potshots at Cain's expense he doesn't take, and anyone else's besides.
This book deals with the eldar (the smug and condescending pointy-ears), with Cain and the 597th Valhallan Regiment aiding the local Planetary Defense Force in keeping them from taking over the planet. As always, there are hints alerting the careful reader as to what is really going in, but as the memoirs are, if not quite stream of consciousness, definitely overwhelmingly cast in Cain's personality, it's easy enough to miss those hints (as Cain does). Ultimately, for those who have read the Cain franchise before, or fans of the old Flashman series, I'd say it's definitely worth reading.