Line of Sight is now traced from one model's body to another model's- no more drawing from the eyes/head. Sort of.
“Start of the turn” is explicitly before the Movement phase occurs; “end of turn” is explicitly after the Assault phase.
Coherency, as several others have noted, is now 6″ vertically at all times (not just in ruins.)
If you generate all your powers from one discipline you get the Primaris automatically, but if you gain a power later from another discipline, you'll lose that Primaris. Chaos Marines/Daemons always know the primaris from their god's discipline.
Force is not a discipline and doesn't count for psychic focus, etc. It is, however, a Blessing and can be negated, etc, as normal.
Warp Charge counts all units on the table, including those in transports. The psychic phase ends immediately if the active player runs out of warp charge.
You can only ever manifest psychic powers on your own turn. Kinda breaks a bunch of the Blood Angels/Grey Knights powers?
Psyker units can only attempt to manifest a particular power once. Text is a little ambiguous what this means, though; if there are multiple psyker models within a unit (that can each manifest separately, as opposed to a Brotherhood) maybe they can each do their own thing? If unit = unit in the normal sense, though, that implies that powers are “shared” amongst a unit, so you could choose to have a unit of Farseer + Warlocks manifest one of the Farseer's powers through a Warlock. I'm thinking that's not how it works.
Deny the Witch is on 6s unless you have a bonus. Shutting down powers is really, really hard. Casting them is harder too, though.
Can't cast anything but Witchfires out of a transport.
Perils only happens on natural double (or more) sixes. Currently there's no way to get modifiers, but could eventually be relevant.
Perils is more dangerous than before, at least by a bit. Still causes a wound most of the time (but on 5/6 you can make a Ld test to dodge it.) 4+ on the table ONLY causes a wound, so not all that dangerous. 1/2 are potentially pretty bad, with 2 actually being the worst- no roll to avoid it, and for low-Mastery psykers it can render them useless for the remainder of the game.
Psychic Pilot explicitly gives a bonus to Deny rolls.
Psychic Hood is 12″ range now, otherwise does the same thing.
Blessings don't stack unless specifically stated.
Conjurations bring the unit in via Deep Strike, so no movement/assault. Mishapping lets you place them anywhere you want on the subsequent turn, though. The conjured unit generates powers/abilities immediately as appropriate, but can't cast conjurations of its own that turn. They're scoring. Conjured Daemons can always take an Icon/Insturment/Champion for free if you have the appropriate model available.
Powers last from one psychic phase to another, unless otherwise noted, so Blessings will never help you on your first movement phase. Interesting.
Maledictions don't have the same “never culmulative” text that Blessings do, but are otherwise worded similarly (which implies they probably don't stack.) Still can't go below 1 in anything.
You can cast as many Witchfires as you want and still shoot, and can target anything you want.
Beams don't reduce in strength anymore for multiple models? Pretty sure that was a thing previously.
Focused Witchfires get to choose their target if you roll more successes than you needed to cast the power. This is huge, as it means that the previously-unreliable targeting aspect of them is now actually quite accurate. They otherwise hit the nearest model, which is still useful.
Novas hit FMCs/flyers.
Shooting is resolved one weapon at a time now, but you can still only fire one gun unless otherwise noted. Interestingly, different fire modes are counted as different weapons for this purpose. The limitation on firing one gun is no longer specific to the shooting phase.
Snap Shots are always BS1, unless specifically stated otherwise or modified by a rule that states otherwise.
If models are equidistant from the shooter, the owner chooses which to remove.
You can't allocate wounds to models out of LOS. [черт] you, blast weapons, you have to follow the rules.
Since weapons are resolved one at a time, it's possible to put your shorter-ranged guns out of range. Pick your order carefully.
Models that Go to ground can't fire overwatch. That's a pretty big deal.
Cover is always 5+ unless specified otherwise.
Ordnance weapons can never fire Snap Shots. Nonvehicle models that shoot an Ordnance weapon can't charge or fire other guns.
FMCs can theoretically drop bombs now. Huh.
Primary weapons with Armorbane roll 3d6 and pick the two highest. Nice little fix there.
You're allowed to charge things you can't hurt, explicitly so.
Charging through terrain is -2″. This can cause you to fail a 1″ charge.
Pile in during assaults is slightly different. Functionally pretty similar, though.
Monstrous Creatures can never Go to Ground.
FMCs that Deep Strike are always considered to be Swooping.
Grounded tests are only on unsaved wounds, and are at the end of the phase. You can't charge if you went into Glide mode on your own turn, but you can if forced by a Grounding test.
Vehicles are allowed to make Snap Shots with ordnance weapons.
When Immobilized, flyers crash on a 1/2 and otherwise count it as Stunned.
Exploding vehicles no longer leave craters. Wrecked vehicles are not dangerous terrain (though they're still difficult.)
Vehicles are allowed cover saves against weapons that inflict damage results, but don't roll on the damage table- specifically including Graviton weapons.
Stationary vehicles are still treated as WS1, though Immobilized ones are not.
If a vehicle suffers a damage result that doesn't kill it, embarked units have to make a Ld test at the end of the phase or be only able to fire snap shots.
Damage from vehicle explosions on the inside is allocated randomly. [черт]ing random allocation.
If a transport is destroyed by a shooting attack, ANY unit that shot the transport is allowed to charge the disembarked squad.
Moving Flat Out while zooming gives you 12″-24″ of distance.
You can't disembark from a chariot, period. Coming back to life if you were mounted on a chariot brings back your chariot with 1HP. When a Chariot is shot at, the owner gets to choose whether the wounds hit the chariot itself or the embarked model (except for blasts/templates, which always hit the vehicle.) Skimmer chariots don't need to take Dangerous tests for charging, and chariots only take a glancing hit from dangerous tests. Chariots (or more specifically their riders) fight like infantry models and the chariot can sweep, pile in, etc, as normal. When fighting against a chariot, you have to resolve all of your attacks against either the rider or the vehicle- you can't split them. You use the WS of the rider to hit it, and grenades can only be used on the vehicle. Hits against the vehicle are always resolved on front armor in CC.
Walkers no longer get a free pivot in the shooting phase. They do have the Hammer of Wrath rule, though.
Ramming does a base damage equal to half the armor facing of the vehicle, +1 for being a tank, +2 fr being heavy/superheavy- speed no longer matters (though you must go as fast as possible.)
Dozer Blades add +1 to your effective armor value when ramming.
Wounds from a challenge spill over into the unit, and wounds from outside the challenge can spill “into” the challenge (but only after all other models have been killed.)
Area terrain as a thing is gone, but many of its functions still exist. For example, ruins provide a 4+ cover save regardless of obscurement.
Craters are 6+ cover, regardless of obscurement, and give +2 when going to ground.
A model that fires a Gun emplacement can't fire any other weapons.
Buildings have HP now. 3/4/5 for small/medium/large. Jump and jet pack infantry can get into buildings. Buildings are explicitly treated like vehicles except where noted otherwise. Units on the battlements of a building that Collapses don't have to get off; those on a Detonating building get a free 6″ move to place themselves legally.
Gun Emplacements placed on buildings count only as Emplaced Weapons and can't be destroyed by shooting at them directly.
Unbound armies are stupid. really, really stupid. They're allowed to take Formations (and gain their benefits normally) if they want.
Whatever detachment contains your Warlord is your primary detachment, but otherwise it can be any of them. In an Unbound army, all models from the same faction as your Warlord benefit from their trait.
You can take any number of detachments in an army, including Allied detachments. “Combined Arms Detachment” is the general name for the old FoC chart, which includes one fortification and one Lord of War. A CAD can reroll its warlord trait and benefits from Objective Secured; allied detachments get Objective Secured, in both cases for Troop models only. Note this applies to dedicated transports for troops.
Warlords can be non-character models, but if they are, they do not get a warlord trait.
The warlord tables are mostly the same, but slightly cleaned up. Strategic is really, really good now.
Unbound armies still need to follow the rules for differing ally relationships. Battle brothers can embark on each others' transports now. Desperate Allies don't cause planes to crash anymore, but are scoring. Come the Apocalypse are like Desperate, but can't be deployed within 12″ to start.
Fortifications are set up with the rest of the army during deployment.
Winner of the roll-off picks whether to deploy first or second, and then both players do so. Whoever deployed first then chooses whether to take the first or second turn. This… is a pretty big change.
Conceding is now actually in the rules, and results in a crushing victory for the continuing player.
Only scoring units can claim Linebreaker. If both players kill a unit at the same time, they both get First blood.
The roll-off to place objectives is done before choosing table sides or deployment types (except in Emperor's Will) and is separate from the roll-off to pick sides, etc. Objectives can be on top of, but not inside of, buildings.
Swooping/zooming units don't score. Nonscoring units can't contest objectives.
Sabotaged objectives now cause d6 hits to units in 3″, rather than the large blast marker. Grav Wave Generator now subtracts two from charge rolls, and is cumulative with terrain.
Night Fighting is ignored if neither player wants to use it. It simply gives the Stealth rule to all units.
There is no limit to the number of units you can place in reserve, though if you have no models on the table you will still lose at the end of a game turn. Units from reserve can manifest psychic powers as they please.
You can't roll the same Tactical Objective more than once during a game. Maelstrom of War missions are optional, and only they use the Tactical Objectives. You generate tactical Objectives at the beginning of your turn, depending on the mission.
Scouring and Big Guns still give VP for killing the requisite unit types, but no longer have anything else special about that type.
The Relic is now scored like any other objective and can only be passed once per turn. Vehicles can never pick up the Relic.
The Maelstrom missions are… interesting. Above and beyond the other stuff here, they're gonna get a post all their own.
ATSKNF no longer gives the free 3″ move for regrouping.
Blind can only cause one test per phase.
Barrage weapons can only fire at targets inside their minimum range by firing directly.
Destroyer weapons always cause no effect on a result of '1′. 2-5 cause d3 damage (HP or wounds) and allow cover/invulnerable save as usual. 6 is the same as before and no saves of any kind can be taken, although special rules other than FNP can still be taken as normal. Destroyer weapons count as S10 for purposes of Instant Death (sorry, harpy/DP, no more dodging that bullet.)
Graviton weapons do nothing to buildings.
Hammer of Wrath is resolved against the armor facing you hit.
ICs can never join a unit that contains a monstrous creature of vehicle. They are, however, allowed to join units that consist of a single model.
Infiltrators and Scouts can never charge on their first turn, even if you went second.
Poisoned weapons only grant a reroll on wounds if your Strength is HIGHER than the toughness of the model you are wounding.
Precision Shots are only on sixes.
Rampage doesn't work when multicharging.
Skyfire no longer allows full-BS shots at ground targets if you have the Interceptor rule.
Smash Attack is now only a single attack, not half your normal number.
Sniper weapons are no longer Rending against vehicles and merely count as S4.
Strikedown doesn't lower the initiative values of affected models anymore.
Supersonic doesn't prevent you from entering Hover mode.
You can use Grenades against Gun Emplacements.
Defensive grenades can be throw as S1 Blind Blast weapons. They don't give Stealth at close range.
Like the missions, the psychic powers deserve an article all their own. (Also, we need to find out who can actually use what tables before they mean much- remember, in 6E a lot of models from a faction didn't have access to all of that faction's psychic disciplines.)