Watch the teaser video here (http://www.games-workshop.com/gws/wnt/blog.jsp?pid=3300070-gws)! Sadly, it doesn't give much information, but we can look forward to the first book (and presumably miniatures to go with it) this August.
Since they made rules for a Daemon Angron, I will assume they're going to have normal Primarch rules and change some over to daemons...
Hopefully, these won't be game-breaking...
I am ultra excited. When I saw this yesterday I started to wonder what they could pull out for this and what new models they could release, another thing I find interesting is that they said Book 1 this Autumn, which makes you believe there will be more then one book.. and if that's the case what comes first? What other pre-heresy stuff could they release? Obviously Primarchs is one thing that comes to mind but what other models could we be looking at? Could we finaly see the much anticipated Stormbird?
I don't know, I'd love to see some Primarchs but sadly the one I want is dead so in a game it would be silly for him to be there... dang. More Daemon Primarchs would be cool, maybe we could see a snakely Fulgrim or deathly Mortarian... although my mind figures they will still hold their Primarch forms if it's Heresy, whcih means we'd see the Twin Primarchs possibly... I am DEFINITELY excited on this one.
Considering the scale, of the Heresy, spreading it out makes sense. Like The Siege of Vraks and The Badab War the books will likely be split chronologically. With that in mind, book 1 will likely give us general rules for playing games of Warhammer 30,000, including how to adjust all armies for doing so (not just Imperial ones), and will represent the Great Crusade itself. Book 2 will likely include the end of the Great Crusade and the seduction of Horus and the others and the start of the civil war with book 3 being the latter parts of the Heresy itself.
We'll likely see rules for Primarchs but I'm not sure about the rules for Daemonic Primarchs; IIRC those Primarchs didn't ascend to true Daemonhood until after the Heresy itself, but may still have enhanced attributes compared to their initial appearances.
Warhammer 30k for non-Imperial armies, huh? Tau Spearchuckers. Can't wait. :P
Considering the number of enemies the Imperium battled against during the Great Crusade, I wouldn't be surprised if they say "you can use your Tau Empire/Necron/Tyranid/etc. army to represent this other army from that time period". That's what the Tempus Fugitives did a few years ago when they ran their Great Crusade campaign weekends, in the lead up to their own Horus Heresy campaign weekends, at Warhammer World.
Edit: Looks like I might have been a little off the mark; Bell of Lost Souls has some information (http://www.belloflostsouls.net/2012/07/40k-news-horus-heresy-forgeworld-details.html) from Chicago Games Day. Needing only the core rules is an interesting, but probably necessary step. Making everything self contained means that FW can run wild and not have to worry about balancing it against the current codexes.
i want an official model of the emperor, not for gaming really, but for the pure awesomeness to paint up and place on my shelf. Horus would be nice too.