Ensemble Dark Horse: Culcis of the Royal Volpone. Mainly due to him assisting the Ghosts in defending his wounded comrades (despite being wounded himself) as well as not engaging in the petty discrimination that the rest of the Volpones did. Him successfully pushing back a vicious assault in Necropolis, losing a hand in the process, did nothing to hurt his popularity.
Fan Nickname: Liijah Cuu is, quite accurately, referred to as Teamkill McBackstab von FethingBastard.
Hilarious in Hindsight: In the beginning of the second book, Gaunt asks Caffran about his fiance, who died on Tanith, and tells him he's sorry for his loss. Caffran sneers and asks if Gaunt is going to give him some platitude about how there's other fish in the sea, and Gaunt sarcastically obliges, telling Caffran that on one of the battlefields he's going to face, he'll find the love of his life. Funny thing is, Caffran actually did meet Tona, the love of his life, on the battlefields of Vervunhive.
Moral Event Horizon Lijah "That Damn Bastard" Cuu crosses it when he rapes and murders a civilian woman in The Guns of Tanith.
Lets face it, he leaps gleefully over it in every book since his introduction, sometimes twice. Honour Guard is notable for being the only book in which he DOESN'T cross it.
There's also Meryn's pension fraud racket, taking advantage of dead Ghosts and relatives for financial gain. Plus leaving Costin to die in order to keep him quiet, not to mention a few other Ghosts who hadn't even been involved in the scam.
Tear Jerker: Bragg and Caffran's deaths are probably the hardest hitting.
Values Dissonance: The morality and attitudes of the main characters owe more to 21st century "Western society" than that of the 41st Millenium Imperium of Man, likely in order to avoid making them all completely unsympathetic. Gaunt puts up with minor heresy, rarely executes soldiers, and isn't a religious fanatic - not the kind of behavior that is encouraged in an Imperial commissar. More representative attitudes can be seen in Commissar Kowle from Necropolis, a Trigger Happy psycho.
The novels also downplay the threat of Chaos taint compared with a lot of other works in the setting - soldiers don't generally become completely unhinged by seeing one Warp-horror too many, and it takes concentrated efforts on the parts of Chaos forces to corrupt large numbers of humans. So, there is no need for the more typical Imperial ways of keeping troops in fighting shape. The Ruinous Powers are still quite potent, and the third arc deals repeatedly with the peril of The Corruption, but humans in the series aren't generally driven to monstrous deeds just to survive.
It's also important to note that the Ghosts are fighting on the Crusade's second front (in a time when there's probably more than one Crusade-sized effort in the galaxy). This suggests that the Warp is not quite as formidable in the Sabbat Worlds as it is in some areas, such as those around the Eye of Terror.