I must say, before I heard of Ciaphas Cain, the Warhammer 40000 universe was a bleak, serious and cynical one in my eyes. Indeed it is dark and scary as it is usually described as. In the background materials. Ciaphas Cain just so happens to capture the atmosphere of the tabletop
itself as well as the backstory, and manages to throw in a fair deal of the black humour that makes the game so fun to play into the grim darkness of the story. Indeed, I was surprised that a book series such as this one existed in such a setting, and when I saw the added title of "hero of the Imperium" written in all caps every time it was mentioned on the wiki, it did not only set the message that it was obviously comedy, it itched my curiosity like hell. So I decided to check it out, and I did not regret it.
As it is already obvious, the Ciaphas Cain series goes for a more lighthearted and comedic take on the franchise rather than the deadly serious portrayal we see in other series. While there are still undertones of the grimdark we are used to in the setting, the Ciaphas Cain series takes these out of a first person perspective from a cynical, snarky, self-preserving and cowardly individual who just so happens to have the occupation of a commissar, and with a very huge streak of bad luck that winds him up with the title of Hero of the Imperium. This practically sums up the titular character Ciaphas Cain in a nutshell, and he constantly has to put up with a good image for the sake of his reputation which he personally believes he did not deserve. Always followed by his odourous but very loyal aide, Ferik Jurgen, the whole Valhallan 597th regiment under his command, it gets hilarious to see him get constantly thrown into dangerous situations simply because of his overblown reputation.
One thing I personally like in the books is the level of detail they go into more trivial things, usually through Amberley Vail's footnotes throughout the books, such as social aspects of the imperium, and certain insight into various events plus a fair amount of references to books by other Black Library authors, like Dan Abnett's Gaunt's Ghosts
series. This indeed gives the series a whole lot of depth into the Imperium's social structure, showing that certain cultural aspects are not so different from ours even in the future.
A must read for any Warhammer 40000 fan.