I had mixed feelings on this one. On one hand, it was fun reading about four of the primarchs involved in the Heresy. On the other hand, one of the stories was good, two were so-so, and one just bored me to tears.
The best was the last one concerning Omegon/Alpharius, although it took me a bit to realize that Sanders was jumping around in the story time-wise. The deception used by the Alpha Legion on both sides was very clever. The first and third stories concerning Fulgrim and Lion were ok to read, just not up to what I have experienced so far reading the Horus Heresy. I did enjoy how Fulgrim's Slaneeshi possessed body was dealt with and how Lion fought the forces of chaos in the warp as he fled the Night Lords.
The story concerning Ferrus Manus did nothing for me, did not advance any character in this portion at all. I've always read short stories with some trepidation as I feel that a lot of times there is simply not enough time to develop plot and characters to a sufficient degree as in a full length novel. This also seems to be the case here as all four authors in this collection seem very rushed or otherwise non-committal to the overall story. Here's to hoping that the next Heresy novel avoids this.