I'm almost finished reading The Horus Heresy: Collected Visions, a compilation of the four volumes containing the history of how the warmaster Horus betrayed the Emperor and the Space Marines, and the battles that took place in the heresy era.
When I was a child, this story were a mere few pages explaining that the warmaster made a pact with Chaos, and converted four chapters of space marines, with vage details of what happened, except that the Emperor defeated Horus but resulted heavily injuried in the battle.
This (big) book extends the history, explaining and telling how was the conversion to chaos, how he defiled the emperor and converted the four chapters to embrace the chaos forces, and even the status and inner battles of the Cult Mechanicum at Mars.
The first two volumes are a bit slow, repeating some tales and advancing slow in the events. Then, the action speeds up and gets a better pace.
The book is full of illustrations, some of them quite good, some decent, and a few ones really bad. The bad ones are mostly sketches that seem to be full-page just to fill more pages of a single image instead of written content, but overall I enjoy reading it.
One point against the pictures is the inconsistency of some of them. Those who, like me, have played Warhammer 40.000 since the 2nd edition, probably know that until then, the Space Marines used the MKVI armor, and had Rhinos and Land Raiders. In the second edition, MKVII armor is the standard, and few years later Games Workshop remade the Rhinos and Land Raiders to "MKII" models, similar but with visual differences.
Some of the artists seem to have focused just on the newer armors and vehicles, just drawing them with the chaotic chapter colors, or placing just one or two different details, which gives a "historical" inconsistency with the technology at that era.
Same happens with Terminator armour and Dreadnoughs: Some of the pictures represent really different and ancient-looking armors, while some appear to be too similar to the current venerable dreadnoughs and termies.
Apart from the inconsistencies, overall the book is good. It is not too expensive so if you like to get a deep understanding of the events that led to the current Chaos Space Marines I recommend this book.