There are tons of leaked photos now, none of which I can post here since GW might sue us (it's happened to other sites). Lots of cheap infantry with good armor and feel no pain, lots of crazy weaponry like triple shot plasma guns. The chicken lancers have kinda lousy rules and the kits are very expensive, the dragoons are quite good for anti-air work.
What isn't known is how the Doctrine Imperitives work. Since some of the infantry is so good and because of how the Horus Heresy Adeptus Mechanicus stuff works, I presumed that they were a penalty system similar to Tyranids and Instinctive Behavior. Recent rumor suggests, actually, that it's a bonus more like Orders for Imperial Guard. One is rumored to give +3 ballistic skill to all units with the Imperative rule for that turn.