Quite frankly, this is a little disappointing. The Horus Heresy book series has all got a little disjointed and shows a distinct lack of direction. A couple of the stories are from well before Horus Rising, most are "current" in the timeline. Even the ones that are current don't really tell you much, and could almost be set in 40,000, not 30,000.
As most have already mentioned, some of the stories are good, some are a bit below average. GW/BL need to find someone who is able to draw it all together, because it's limping on pathetically at the moment.
My ratings of the stories. A * at the beginning highlights those that are set before even Horus Rising.
BLOOD GAMES 9/10 - As usual, Mr A keeps you guessing. Sets some groundwork, and perhaps we'll see the title charactor again. Unlikely, but you can hope.
WOLF AT THE DOOR 8/10 - Quite a good story. Plenty of action, and a nice twist at the end.
* SCIONS OF THE STORM 3/10 - Probably the worst of the bunch. The Word Bearers just aren't quite crazy enough in this one. Set too early too.
THE VOICE 7/10 - A good story by Swallow, but it does nothing for the Heresy arc. A bit like Blood Games really.
CALL OF THE LION 7/10 - By far and away the most relevant. Nicely written, but could possibly have gone further.
* LAST CHURCH 8/10 - No real relevance to the heresy, but it does explain the reasons behind the crusade as a whole.
* AFTER DESH'EA 5/10 - An OK story, though not to my tastes. It doesn't really mean much, I mean we all knew Angron was crazy.
So, all in all, buy for completeness. But it's starting to get to the stage where that's being said too much. Still, you would hope the next couple of books (Fallen Angels by Mike Lee, A Thousand Sons by Graham McNeill and Prospero Burns by Abnett - the latter two telling the same story from both sides) will bring us bang back in line with what "should" be happening. I.e. the Horus Heresy...!