I'm pretty excited about this - compared to the many who've written about DA (even in passing), I think Gav's is the most solid and engaging take I've found on them. The Unforgiven in particular I found to be very good indeed.
That said, he's also writen a few I'd be less effusive about (Ravenwing, Kadillus), but that's more because I found them to be fine for my tastes, just not particularly nice. (In contrast again to the likes of the Path of the Eldar series, or The Red Feast etc.)
Even saying that, I do find his prose to be distinctive from others' - 'drier' is how I usually describe it. If you don't like that, there's no sense in calling it bad, if what you mean is it's not to your tastes.
But then I don't think many people (myself very much included) can even perceive their own tastes, let alone can properly distinguish the technical aspects that work and don't work and how they factor into them.
i've read the first two ahriman, which i dig, but for some reason doesn't feel like a tsons book to me so much as an ahriman book? not really sure why
What I said above for Gav can be applied with John too - he's a distinctive writer, but that distinctiveness can be divisive too.
I think there's a lore-based reason that the Ahriman stories don't really feel like a Thousand Sons story: they aren't. Ahriman is to the Thousand Sons as Slaanesh is to the Aeldari, or Archaon is to the old Warhammer World. He's their doom, not their shining salvation.
He's wrapped up inextricably in their fate, and is fundamentally a part of their story.
But the character of Barry Thousand, Son of Magnus, whose life and works are all about expanding the fiefdom of change and magic and arcana to progress their own standing on the Planet of the Sorcerers?
That's a fundamentally different story to the story of Ahriman.
It's, in some respects, a good illustration of a possible avenue that Gav's story might take too: how much of Luther's story is fundamentally a Dark Angels story, and how much of any story of the Dark Angels is inherently also a story (sometimes in negative/omission) of the Fallen?
They're linked in quite deep ways, but one is not really the other if you get me?
Or not necessarily, at least.
I think it's a touch sad that very few, if any stories really get into the other spaces that the Dark Angels inhabit, and manage to make much of anything without the Fallen being a feature.
The Wrath of Magnus and the Ritual of the Damned is maybe the closest that angle's come in breaking away from being all about the Fallen?
(It's arguably an odd switcheroo with the Space Wolves, transitively linking that because Dark Angels rival Space Wolves and Space Wolves rival Thousand Sons, there's gotta be some story in the Dark Angels rivalling the Thousand Sons too? Could have been different again, a strange "rival of my rival is my friend" angle, where the Thousand Sons and Dark Angels' penchants for secretive, obscure, hermetic conspiracies plays a significant part? But even that's not really touched on, it's just played straight: Dark Angels get caught up in it because they begrudge the Wolves, and somehow get swept along into Ritual of the Damned too because, y'know...?)