Warhammer 40k is both very, very cool, and very, very dumb - it is the very specific combination of positive and negative factors we refer to as "sweet." Destiny is kinda sweet, right? You're catching air on your jetbike in view of a passel of weird-ass moons, and even though you are an immortal space warrior you have a machine gun and a bunch of feathers poking out. In 40k, people fly around in huge churches that are so big there are people in the belly of them that think the outside world is a myth. They have Space Vikings and Space Vampires. Acquisitions Incorporated can hit some real drama precisely because it's incredbly goof troop for the majority of the runtime. Somehow, being silly in some ways - unabashed - allows Games Workshop's cadre of writers to pull out some gruesome gut punches. Magnus the Red falls in that category.
Even the backstory for all this shit is a million books, and to actually understand the fullness of the strip would require explaining things like The Council of Nikaea, how magic functions in the material universe, a brief primer on cosmology, the fundamentally Promethean nature of the Emperor's project to create the Adeptus Astartes, the fact that the Adeptus Astartes are also called Space Marines, maybe a quick detour into the Narthecium perhaps, the idea that there was a Fall like Lucifer's fall that split the Space Marines into Loyalist and Heretic factions, and that each group of Space Marines has a kind of Father they're based on. I can't really do that, and I wouldn't want to anyway, because these things need to be experienced in context.
The main thing to understand is that being a father is hard, and being a son is also hard, and Magnus had the opportunity to be ground to dust between the heat and pressure of those two states. The whole thing is pretty sweet, honestly; it would look great on the side of a van.
(CW)TB out.