here's a rundown on the manga: it's a direct spinoff of the Drakengard series; I wouldn't recommend reaidng it if you have no experience with either of those games, because it won't make any sense. the manga precludes that you already know the major characters (One, brother One, Furiae, Caim, and the Black Dragon are recurring; Nero is new), lore, and previous story and explains very little otherwise. the purpose of the story is to bridge the gap between the timelines of Drakengard 3 and Drakengard.
pros:
- fantastic artwork
- filling holes in the lore and development on existing characters and concepts, particularly the Red Eye Virus and the Black Dragon's machinations
- more context for the setting of Drakengard 1
- we get to see what One's brother has been up to (being sad, mostly), isn't that fun?
cons:
- even in a series built over a foundation of putting irredeemably awful people into the places of heroes, Nero stands out as particularly unlikable
- weak/unclear character motivations, which makes the story unfocused and at times confusing
- pretty much all of the rape scenes are kind of unnecessary and could have been removed or reworked with little narrative value lost. there's a a lot of killing, but that's about par for the course. however, the manga puts very little effort into tying this all together thematically compared to the games, so it all feels sort of gratuitous.