When the Horus Heresy books started coming out from Black Library, I was pretty excited. "We're finally going to have a really in depth telling of this interesting bit of 40k history", I said to myself. I read the first book. Pretty solid. And the second. And the third. And the 20th. And the 30th. I completely gave up once the series became totally unmanageable. It's one thing to just read a particularly long series of books. It's another when that series of books is really a dozen different sub-series told through books, audiobooks, short stories, novellas, etc. It's impossible to stay on top of all the releases. I tend to be the kind of person where if I can't read a whole series, I don't really want to read any of it.
I think book 32 or so is the last book I read. Book 41 just came out. I totally bought it... with no debate at all.
I'm about 2/3 of the way through and I'm enjoying the book so far. I was really hoping I'd see more background into the actual Emperor's history, but I think they're keeping that purposefully mysterious. Granted, I still haven't read through to the end of the book. What I can say is that it heavily features the Sisters of Silence, the Custodian Guard and the Mechanicum. I'm a huge Mechanicum fan, so I'm chalking this up as a win so far.
If you like the Horus Heresy, but aren't particularly interested in reading about Space Marines fighting Space Marines, I'd give this one a shot.