I'm a few days late with this one, I blame it on the shock of how awesome this looks. Once again I'll be heading to Birmingham in under a month now to gab myself a copy. In the mean time here's some screen grabs from the teaser video to drool over!
The book itself

The dropsite Massacre
Iron Hands
Night Lords
Salamanders
Word Bearers





From what I can tell there's going to be a huge amount of new units in this book. A smattering of generic add-ons to the Legion list from book 1, a few more Mechanicum units but still not a full army, and a lot of legion-specific units. Here's what I've got so far -

Generic - Sicaran Battle Tank, Javelin Attack Speeder, Glaive, Fire Raptor (although it could be Salamanders)

Mechanicum - Magos Dominus, Castellax Battle-Automata.

Specific - Erebus, Kor Phaeron, Ferrus Manus, Kakophoni Noise Marines, Phoenix Guard, a new unnamed World Eaters unit.