Here is a rundown from White Dwarf what the Horus Heresy Betrayal at Calth is and what it contains. This is going to be a big release, and will sell a lot if not for the board game (which I am also interested in), but for the models themselves. Apparently you can upgrade their shoulder pads to your legion!!! Whoa. Did GW just give us reason to buy more than one of these board games?
via Tanaka Tomoyuki
Ancient Armor in Warhammer 40,000
The Horus Heresy: Betrayal at Calth is an amazing board game, but it's also a sensational addition to your miniatures collection, loaded with 30 Tactical Marines, five Terminators, a Space Marine Captain, Chaplain and a Contemptor Dreadnought.
The Space Marine Chapters fighting in the 41st Millennium cling to the relics of the past out of a mixture of reverence and necessity, faithfully maintaining older marks of armor and weapons, so if you want to bolster your Warhammer 40,000 Space Marine army with the models in this boxed game, you can.
The models in the set are also fully compatible with Forge World's range of Horus Heresy miniatures (as they are with all the plastic Space Marine kits in the Citadel range), which means you can upgrade them with Legion-specific shoulder pads and weapons. So, if you're looking to add more squads to your Adeptus Astartes Legions for Horus Heresy battles, you'll find these new plastic miniatures equally useful.