Yeah, I know what you mean. The Horus heresy series seems to have had poor editorial oversight, the number of just vaguely relevant sidestories spinning out of control. Such as the extreme focus on the shattered legions or Calth. For not to talk of the truly massive amount of limited edition novellas, whereas only a bare number of them has had truly plot relevant stories that wasnt meaningless in the overall context.
Though highlights of the recent years for me, has been the dark eldar path series, as well the Ahriman books. Both have been downright awesome.
Ive been enjoying the Beast Arises stories, and the layers of revelations that have been comming. Seeing the glimpse of the Imperium that was in the great crusade as the rot set in. And the dramatic miscalculation guiliman made when he split up the legions. Drakan and the terran politics have been a blast to read, though i agree, its beginning to drag a bit now, feeing samey and having lost the initial wow sparkle. Drakan was a lot better protrayed in the initial sets of books, as well his schemes. Such as poisoning the eclechiarch or trying to outwit the high lords. Brilliant. But Koorland has pretty much taken center stage, and you can see how quite out of his depths he is with politics, whereas Drakan sadly has become more of a supporting character. Hopefully that will turn over soon enough, for his own explosive finale book to come.
TBA have had hit and miss books, but so far im greatly enjoying the series for exploring this period in time that nearly sunk the imperium. Who knew the orks could be so scary?
TBA has also been much better planned, a set number of books, all written in advance to be doled out over a year. The heresy could learn from this approach.