Always good to have feed back of course and I do appreciate the quick review
As my ratings indicated it is above average by itself but as the start to the series as a whole and (admittedly I am breaking my rule about not thinking about the books to come) it is a gripping book. 6/10 by itself isn't bad at all, as a piece of background, which you mention, it is one of the best in the series though at 8/10. To be fair I have only three books that count as above a 9 to me so it IS a good work and as many have indicated it is part of a trilogy kind of.
The reason for the low stand alone rating is because, like Iron Man 2, it sacrifices a lot to drive the story forward. It is a great start for the series but if you read it and stopped it wouldn't be the best of the lot (to my mind that would probably be The First Heretic or a Thousand Sons).
I agree about Loken incidentally, he IS a strong character (and gets oh so much better as the series continues). I like that he is the straight man though at times he's just a tad too stiff in his bearing. Still he is dynamic and interesting. About the other legions I suppose I was taking it that since Tarvitz is the one narrating his own story that it was how the Emperor's Children actually were. I really like Saul in the next books but he does feel a lot like Loken to me, not a bad thing as I do think that he is a good straight man. The EC just don't sound all that nice, even the book mentions this with one of the Luna Wolves remarking on their haughtiness so I feel my thoughts their are at least well founded.
As to Chaos, I do get it that they don't know but from both the micro view I am affecting and the macro view of the series as a whole I NEVER understood exactly who knows what about chaos. Mortation speaks of sorcerous powers and how terrible they are, Magnus' Sons use Tutilaries, and in living memory (for some) such daemons have been summoned and yet the Luna Wolves know nothing about this? It just strains my belief a little too much. Granted that this is a question that will never be answered but I don't understand why you wouldn't tell the SMs about the dangers of Chaos. Not doing so is what brings the whole thing down any way. Pet peeve perhaps :p
Also on the subject of Chaos it DOES have a foothold (and Fulgrim is awesome btw). A lot of the stories that come up later in the series show strong chaotic evidence. The Laer as an example, the wraith singers in the next books, Mortarion's home, The world that the Alpha Legion are fighting on (that black cube and all). It is around and it was fought, they mention fighting similar things several times throughout the series.
As to Horus fighting on Murder I get his ego and I understand how the martial honor thing works but it was just shortsighted. I would see it if it were and Angron or Mortarion or even Russ but Horus is supposed to be a strategic genius of the first order. This doesn't show that. It also served no purpose. How would the effect on the story have changed if the Interex had showed up just after extracting the EC? The same discussion could have happened and the story proceeded sans battle. That was my beef with it. From a dramatic stand point it wasn't really needed. I would have liked to hear more about the Interex and less about the megarchnids. After all the Interex weapon is of such importance in the coming books that a discussion of the culture that created it should also have a lot of juicy facts. (Ok, I am a bit of a xeno lover)
Samus is an antagonist in that his power is what warped Jubal and caused several deaths, he apparently has been manipulating things at least a little so he just seemed to fit there.
My thanks for the comments, half the reason I wanted to do this was to discuss such things and yours have been quite to the point. I suspect that the next review will solve the issues that you see in this one since it is a strong bridge and enhances the two other books around it. Keep challeging me good sir!