I don't tend to grade the HH books with a score, I still know which ones are worth reading and what ones are not and it's been 5 long years of reading.
A good HH book is..
- One that progresses the story and keeps moving it forward.
- One that has Marine characters that symbolize their legions personality. So Garro, Loken, Ventanus, Argel Tal, even super arrogant jerk Lucius.
- One that has human characters or near enough humans that give us mere humans, IE the reader, a POV into how it is to be a human in those times. Great examples IMO are Ignace Karkasy, Hurtado Bronzi, Koriel Zeth.
- One that doesn't leave even more questions at the end. I like endings that convey the happenings of an event and then stop and don't stretch the damn thing out.
A bad HH book has..
- Nothing but Brother Generic marine in every role that isn't the main Marine role. Nor do I like generic stereotype marines that EVERY legion seems to have, Brother overly abrasive, Brother light hearted, Brother whiny, Brother red shirt, and so forth.
- Human Space Marines and/or assassins. If you have emotions that affect your judgement, you shouldn't be in the uniform. You shouldn't be having feelings and emotions that jeopardize battle's, reports, even making tea. Writers that do this have missed the point of what it means to be Astartes or a super highly skilled assassin.
- An area of the HH that is not important enough to warrant a book so early in the series. Or is of an event that has no hugely significant impact on the story and is (or at least feels like) pure stocking filler.
- Pages and pages of Bolter porn. We get it, marines roll in, things die, marines do amazing things. Does it help visualize how marines perform war? Yes a little, but as the HH is more of a mature story rather than comic book I expect the HH books to know when to put the toys away.
- Moments of Primarch emo crap. Super beings with great wisdom and martial prowess turning into unsure, unconfident teenagers and with the onset of world of warcraft social outcast syndrome can leave their baggage at the door thanks.
I'm sure this is not all of my reasoning but for the moment that will do