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.