GW has posted main rulebook and codex FAQ's. They can be found here. I've only looked at IG so far. Further analysis to be burning up the internets to be sure.
What I see for IG largely makes sense:
Grav Chute insertion works anytime a Valk/Vend has moved more than 6", so it works when zooming
Commissars can't cap allies, while I can see high comedic value...
IG Priests don't affect allies (duh)
Allies don't take orders even if an IC attached to an IG unit.
Rough riders lances explained more clearly
And my favorite: Leman Russes are HEAVY vehicles.