Definitely should read the Heresy series.
I've read all that have come out so far and I am always slavering for the next one. The only one that I thought was a little disappointing was Descent of Angels. It really didn't progress the macro plot line at all and pretty much was just a long explanation for Fallen Angels.
"We are not your worst nightmare.... we are your every nightmare."
The HH series is good. Anything Dan Abnett writes is better. Start with The Founding (3 books in one). You will become addicted to Abnett's writing style. IMHO, he's the strongest talent Black Library has in their shop. Abnett has also written (two I think) HH books. They are among the best ones in the series.
Welcome to the 40k fiction addiction. Don't be turned off by the franchise tie-in. The books are quite good in the their own regard!
I think this is the strength. We've been reading the codex books with the short summary for two decades now, and I am personally ready for a more complete story. I'm heavily into the TTG and Dark Heresy, and the stories on the periphery really have impact on them in the 41st millennium in ways I hadn't expected.
I concure that these are some great reading materials, even if you are not an avid fan of the game. There are some well written scenes that I can't write about without getting the books as it simply wouldn't do them justice. You will understand when you get to the part where a Sons of Horus Marine enters the fighting arena with that pompous Emperor's Children slash-face, or the last paragraph to the Legion Novel I think it was.
As an aside though. Did anyone else feel cheaped out on the corruption of Horus? I mean he gets diseased, has a fever dream and then he's chaotic. It seemed a little too simple for me. I envisioned a long convoluted teasing of the man... I understand the Chaos Gods are powerful, but I thought there should have been a much more elaborate sequence of corrupting the Emperor's favoured son.
These books are fantastic. Every single one of them. Dan Abnett and Graham McNeil might write better than the others but each book has its own feel and brings to life the universe of the 31st millenium. I know it might be a bit redundant to suggest you read from book 1 onwards but really, book 1 is probably one of the best. As you start to get to grips with the characters and the setting, the book ends and so you will no doubt read books 2 and 3 aswell.
If you were to stop there, that would be allright, the fall of Horus is well under way and I guess you could fill in the rest for yourself. Just for example let's say you did actually stop there,well if I knew you and we were out talking about this I think I would be a pretty terrible friend if I didn't say, "you MUST read Legion", because it is one of the best fiction books I think I've ever read.
My little addition would be the flight of the Eisenstein because it is really dramatic and has some great characters plus it finishes off some ends of stories that you want answers for.
LASTLY, books 1-4 are the core of the story, I think anyway. Book 10 I think it is which is a compilation of short stories is also quite good, some nice Emporer of mankind moments in that one.. Legion is a must own, all the others focus on other parts of the greater picture and so you don't NEED to involve yourself or your wallet in those if you don't want to.
I've read them all, I could go on for hours about these books because I love the story.
The Emperor protects.
i would also recommend the Three stories in the two audio books.
"Ravens flight" by Gav Thorpe
"The Dark King" by Graham McNeill and "The Lightning Tower" by Dan Abnett