The Betrayal of Calth promises to be a huge seller, and I don't think that GW can slow this one down from selling out. The demand for it is rather huge, and many people are already getting in multiple pre-orders in with their stores.
Here is a quick overview that was sent in by a good source.
Quick overview of Horus Heresy - Betrayal at Calth boxed game.
38 Brand new, exclusive Space Marine Miniatures -Based on the
storyline form our NY Times Best Selling Horus Heresy Novels -First
ever plastic Horus Heresy miniatures.
-Value of contents is nearly double the retail cost. Prior to this,
only available as resin model from Forgeworld in the UK
-The models are compatible with both Warhammer 40,000 and Warhammer
30,000 (AKA Horus Heresy via Forge World)
-The plastic sprues have multi-pose miniatures with multiple build
options, they are not snap fit models -No specific Legion markings
(This allows you to customize your army and build them as any space
marine legion or chapter instead of just the 2 featured on the box)
-The Box may be built as one single army, or 2 competing forces
depending on your preference.