For those installments in the Heresy that are rounded to-perfection in a wide spectrum of areas a novel of such requires, then anything bearing Dan Abnett`s or Graham McNeill`s name upon the cover its a more than safe bet.
My favorites thus far, being:
Fulgrim, for the interesting insight into the descent of Fulgrim and the Emperor`s Children from perfection to perverse, by narratives from the perspectives of various Remembrancers, the introduction of the Eldar and their awareness of Horus` fall to the Ruinous Power`s, and the sheer-bloody delight that is The Dropsite-Massacre in the finale.
Horus Rising is arguably the most rounded book I have ever read, with no flaws at all, and too many positives for me to begin to describe. I enjoyed Galaxy in Flames for the Virus-induced carnage, although with often the case of novels that are enjoyable, the supporting, non-action elements fail.
Loathed Descent of Angels, though I have faith Mike Lee can finish that dreadful duology off well, and The Flight of the Eisenstein and Garro`s final duel with a Nurglesque Death Guard on Luna, with the ''Terra-rise'' really instills faith in the Emperor`s divinity into you.
Haven`t read Legion, nor A Thousand Son`s, so I`m certainly not as well-read as the above...