I only started with the horus heresy a month ago, so I'm not that far in (though at an acceptable pace, as you can see )
Horus rising: 9/10 good opening for the horus heresy series, paints a great picture of the great crusade in action, including its ideals, how it works in practice (remembrancers, iterators, accepting the imperial truth, etc.) the astartes (and how 'mortals' look at them) andsoforth. Loken's a very likeable character.
False Gods: 8/10 quite okay, but I think the turning of Horus could've used significantly more pagespace and arguments to turn him. We only go through a future shrineworld and the facility of the primarch project, untill Magnus shows up, unveals Erebus and attempts to save him. And yet he turns so utterly and irrevocably. This part could have easily used another 25-50 pages, because it ought to be the critical moment, where Horus falls. After that the book kinda goes on into a lingering epilogue with the auretian technocracy, as the main point of the book has already been passed.
Galaxy in Flames: 9/10 I might be an oddity here in that I might like this one the most of the opening trilogy. The point where it all goes to hell: Istvann III. I greatly enjoyed the descriptions of Istvan III and its warriors, capitol and mythology, the battles the loyalists fought against them, and the great tragedic moment of the virus bombing, where it all gets utterly swept away. Certainly I found the virus bombing a good read, when Tarvitz listens in horror to the horrific sound of millions crying out as they die. And of course the great line; Order the guns to fire. Let the galaxy burn! Istvann III gets scorched into oblivion and this world that was a beautiful cultured world only minutes before, turned into a horrific wasteland. With that image in my mind, the last stand of the loyalists becomes an even more grim picture, where eventually all the likeable characters find their end.
Flight of the Eisenstein: 7.5/10 okay. It was fun to read about the death guard first. Then we get some repeated events at Istvann III, though the moment of the virus strike was far from as tragic as I found it in Galaxy in Flames, because it is only observed from space. The escape and flight through the warp are fun to read, but the 'flight of the eisenstein' itself basically ends after that, and the events Dorn and on Luna drag on a bit too long like a long epilogue.
Fulgrim: 8.5/10 good book, hedonism, mhmmm. The fall of the emperor's children is a bit dependant on plotdevices though, the sword of the laer and the laer temple, but apart from that I think the slide went gradually enough from a search of perfection, to the search for pleasure. I liked the bits with Fabius, and the ending was good (and tragic), even if Istvann V was pushed in at the very end. Around page 400 I thought 'yeez, and they still want to fit the entirity of Istvann V in here?' and indeed the 'dropsite massacre' portion of the battle came and went in 2-3 pages. Still, the moving ending took away Istvann V's slightly bad aftertaste.
5 books in a month, I like this series