I'm seriously addicted. Since I started the Horus Heresy a week and a half ago, I've plowed through 3 books (I'm getting ready to start Flight of the Eisenstein now) and I sincerely love them.
Then there's all that other fluff stuff. I was able to score some Index Astartes books, as well as the Insignium Astartes book. Great, great stuff as well.
I'm hooked.