Now a good question that a friend asked me is, "Well, are these next three books any different from the last three?" And to an extent I have to say no, it's a lot of more of the same. Cain is cowardly and wants nothing better than to get out of trouble but always finds himself ending up in the middle of the largest concentration of enemies he can find. Jurgen, meanwhile, is phlegmatic and loyal and ends up saving Cain's ass a number of times despite never being in the official stories of Cain's life, and Amberley provides snarky comments on Cain's autobiography. So in many respects I will admit this omnibus is more of that pulp sci-fi that I can't get enough of and keep reading.
What is unique about this omnibus and which I particularly enjoyed was the three novels focus on three events which occur at different events throughout Cain's career. We see Cain at the beginning of his career, still with the 12th Valhallan Artillery, and as a fairly brash young commissar who still has yet to become a Hero of the Imperium but quickly finds himself embroiled in an ork invasion. We then see an older and wiser Cain during the middle of his career with the 597th Valhallan facing off against an unstoppable tyranid swarm. Finally we see a very old Cain at the end of his career teaching commissar cadets at a planetary schola, but Cain is pulled out of retirement to defend the planet against the forces of Chaos. Overall I rather liked the overarching story arc of the shadowlight artifact which tied these three events of Cain's career together and added a sense of the long-term effects of Cain's presence in the galaxy. Plus there were plenty of excellent action sequences to keep the most rabid fanboy satisfied.
I will admit that there are a couple of flaws with this book, such as the fact that the stories contained in it don't vary too much from the books in the first one so if you weren't impressed with the first collection you really have no reason to read this one. Furthermore, despite seeing Cain at three points across a century, neither he nor Jurgen change as characters. Cain remains...well...Cain, whether he's a commissar fresh from the schola or a century-old badass, which was a little frustrating. In addition, while I understand why the first novel of this omnibus was in this omnibus, being part of the shadowlight story arc, I kind of wished it had been the first book in the series because then we could see Cain becoming a Hero of the Imperium rather than being introduced to him after he has gotten all sorts of fame and accolades.
Despite the issues I mentioned, I really liked this book and I think it's a must-read for any fan of the 40k universe; I think it's an excellent tongue-in-cheek approach to a universe that often takes itself too seriously while still maintaining the space opera and pulp aesthetics of the original source material. I might even go so far as to say that people new to the Cain series should read the first story in Defender first, followed by all of Hero, and then the other two-thirds of Defender. It might just be my preference for chronological order but I like seeing Cain develop his undeserved reputation as a hero before he becomes a posterboy of the commissariat.