First off, how have psykers changed? Well, in terms of casting, not much. There were early rumours that it's be like 8th edition fantasy, but thankfully it's stayed the same, using your leadership value. The difference is that you must also to expend 'warp points' to cast powers. Warp points are similar, in ways, to focus in Warmachine, in that your psykers 'generate' warp points, to then spend on powers that turn. Each power has a warp cost, usually one warp point, sometimes two. How much you can generate depends on your mastery level. Whilst this is mastery (1) for most, there are some with two, or even three. Luckily for me, Ahriman has mastery (3), meaning three points a turn to spend on shiny new powers.
Oh, did I mention there are new powers? Five 'disciplines' have been added for armies to choose from, ranging from biological manipulation to violent pyrotechnic displays. Whilst armies are limited to what disciplines they can use, all of them have their uses. I'm currently partial to telepathy. I quite enjoy the idea of Ahriman using 'gate of infinity' (a medium range teleport), followed by 'crush' or objuration mechanicum' (which hurts an enemies ability to hit and wound). Whilst rolls are randomised, with mastery 3, I have a good change of at least one dice rolling a power I want. As well as this, you can still choose your existing army specific powers, and in terms of Chaos marines, you can choose to replace chaos powers with the disciplines. But, a bonus for Ahriman is that he generates three powers, on top of having all the chaos powers. So that's about eight powers to pick from? Nice.
Alongside this, most units now have some form of defence against powers which target them: Deny the witch. Essentially, it's a 6+ psychic hood for the unit. Whilst not brilliant, it does help against the more nasty powers.
Now, shooting. For the most part, this too is same-old-same-old. The big change is that heavy weapons can now shoot on the move. Sure, you need a six to hit if you move, but any chance to hit is better than not shooting at all. Also, shooting at the newly introduced 'flyer' type uses similar rules to Forgeworld, in that you need sixes to hit flyers. Unless of course you have the 'skyfire' rule (essentially the old AA rule, again from Forgeworld). Weapon profiles for all guns are now included in the rulebook. Interesting to see autoguns, stub pistols and macro-cannons in there, I wonder what uses them...
Come back tomorrow for part four: Tanks, vehicles and hull points.