Just finished Unremembered Empire. Decent book, I suppose. Explains a lot, or rather sets up (or changes) lore to explain how the Dark Angels and Ultramarines don't show for the siege of Terra. Frontpage is a big misleading, if you were expecting the Angel. Guess that's a spoiler, but if you were fiending for Sanguinius, you deserve to know.
For those who can't be bothered reading it, and those that already have
It's an okay if you're a Horus Heresy lore-whore like me, I guess. If you're looking to just consume Heresy content, then yeah Certainly not a Nemesis or Battle for the Abyss or their like, but the Vulkan Lives arc that made its way in pissed me off. There's some serious and ridiculous weird Mary Sue-ing going on with Vulkan in a, IMO, very very stupid way. The Horus Heresy series has never been any sort of literary work of art by any means, but a several of them were genuinely decent reads if you enjoy the 40k universe.
Lately though, jesus christ. Supposedly all the authors in the series meet up and convene on this shit, but if that's true they all need to get dick slapped. Or whoever's arranging and approving the meeting needs to. They were smoking some serious crack, or watching interracial gay snuff movies when they decided on the new Vulkan shit. Probably both.