1) No surprise here, but Necrons are still essentially Tomb Kings in space fluff wise. A shift in fluff is now that all of the higher up necrons are intelligent while the lower level ones are still basically automatons. I guess that's roughly the same as it used to be, but apparently there is more emphasis in the sentience of the higher Necrons now (hence the named Lords).
2) C'Tan are still in the codex...sort of. They have been moved to the Elites section and are now a single unit choice, but with variable upgrade powers you can take.
3) We'll be Back is no longer called that and it is NOT Feel No Pain. Basically it is a 5+ bonus save similar to Feel No Pain, but doesn't get cancelled out by double strength, AP1/2, etc. In addition, this save is made at the END of the phase after morale tests are taken. If the unit is wiped out or is falling back at the end of the phase, then the save cannot be used. So as an opponent, if you manage to wipe the unit out or make them fall back, then you prevent any Necrons from getting back up...unless the unit has something called the 'ever-living' rule, in which case it gets to attempt this save even if the unit is wiped out.
4) Gauss Weaponry does NOT have rending. It retains the 'auto-glance' on a penetration roll of a '6' rule, but apparently otherwise has lost the 'auto-wound' on a roll of a '6' regardless of Toughness that it used to have. The Gauss Cannon is now apparently Assault 2 & AP3 (I'm assuming the Strength is still 6). The Gaus Flux Arc on the Monolith no longer automatically hits every unit within range, instead each one fires separately and can hit four different targets.
5) Phase out is gone.
6) Destroyers now count as jump infantry and there is a new Fast Attack Jetbike unit called Tomb Blades.
7) Immortals are now a Troops choice. Pariahs are gone. Flayed Ones are Elites.
8) There are indeed 6 named characters (although I have no more info on them). There is also a Necron Overlord and a bodyguard unit called Crypteks. Crypteks can be split off before the game to lead units of Necrons, very similar to Wolf Guard in the Space Wolves codex. Crypteks can take a bunch of different technology upgrades, so there is kind of a way now to have personalized squad leaders in a Necron army.
9) They army is much more mobile now in general. They have several units of jump troops, and 2 new transport vehicles. 1 transport can carry 15 necrons while another can carry 10. Jump pack units count as 2 models and jetbikes count as 5. The one that holds 10 is able to recover casualties to a unit (although can't take it beyond its starting strength). Necron vehicles besides the monolith are open-topped skimmers. However they have something called 'Quantum shielding' which gives their front & side armor +2 until the vehicle takes its first glance/pen, at which point it loses the shielding. One of these two transports (not sure which one) is apparently a personal transport for the Lord (and his retinue).
10) There are six new vehicles in the codex (including the two transports mentioned above). Two of which seem to be based around this old Jes Goodwin design: http://storage.canalblog.com/29/28/731795/53057637.jpg
11) In general Necrons have a lot more long ranged fire support. There is also a new weapon type called Tesla weapons. These weapons, on a roll of '6' to hit automatically cause two more hits. The biggest version of the Tesla weapons has a chance of hitting all other units close to the target; both friend and foe. One of the new vehicles carries the doomsday cannon: 72" S9 AP1 Heavy 1 large blast. BS4.
12) In the Elites section there is a big new walker. It has a heat ray that that is either a melta or flamer depending on what you want to do. Any unit hit by this vehicle is marked (as in: laser targeted), which means that all other necrons count as being twin-linked for shooting at the marked enemy unit that turn.
Okay continuing on here with some nice stuff (added 5/5):
13) Necron Warriors have the same basic statline they had before except they now have a 4+ save. Now before you go crazy, also note that their points cost is 12 points, which is a 1/3 price drop (down from 18 points). That means you get 1/3 more Warrior models in the army for the same amount of points...it also makes losing an entire unit due to sweeping advance, not nearly as painful.
I know a lot of cynical people will hate this and accuse GW from simply making the change to sell more Warrior models, and you could be right. But personally I was always hoping they were going to make Necron Warriors not quite as tough and dump the points cost on them, so you could really take a ton of them...given in my mind they are supposed to be more like a shambling horde of undead robots than some sort of small elite force of super-warriors (but that could just be me).
So this change alone totally changes the army from out of the 'MEQ' umbrella and makes their base statline unique in the game (which is good, IMHO).
14) Immortals have lost their T5 (down to T4), but keep their 3+ save. However, their points cost has dropped to 17 pts a model, which is an 11 point drop (more than 1/3 a drop from the previous cost of 28 pts)!
15) All units in the army benefit from the new WBB rule, not just the units that were formerly classified as 'Necrons' in the current codex (even Scarabs!). So although you're only getting a 5+ save in many cases, you're still getting it on some of the more expensive stuff in the army as well (and there are some pricey new units to counterbalance the relatively cheap Warriors and Immortals). Also the vehicle that can add models back into the unit is also able to use this ability on any unit.
15) Rez Orb is still in the game and boosts the new WBB rule to a 4+ instead of a 5+, but only affects the unit it is in. I have a strong suspicion that this is an upgrade that Crypteks can take (I'll confirm if I find out), so I'd imagine you can get quite a few units in the game getting the 4+ bonus save if you want to pay the points to take them for your Crypteks and then split those Crypteks off to lead units.
16) Veil of Darkness is now definitely something Crypteks can take (so you can have a bunch of 'em in the army), but it no longer allows a unit to be pulled out of combat (and neither does the Monolith), except in the case of the Veil carried by one of the named Lords.
17) In the new fluff it sounds like the C'Tan were mainly killed off by the Necrons (or something like that), so the C'Tan that you field in the game are just remaining shards of their power. They're naturally still a really mean Monstrous Creature who rocks in combat, but you can also purchase a bunch of different abilities. These abilities are in line with a lot of the things we've seen in the last few codexes, things like: messing around with Deep Striking enemy units, making enemies moving through terrain differently, and allowing the Necron player to change some of his deployment, etc. So it sounds like you have a lot of different options with the C'Tan that really mess with the enemy army and/or supplement your own. And they are not one per army (so you can have 3 if you want to use up all your Elites on them, although it sounds like the other Elites choices are pretty awesome as well).
18) Some of those six new vehicles include flyers (not sure how many), which can move at cruising speed and fire all their weapons.
19) Besides a few units that are Fearless (Wraiths, Tomb Spyders and Scarabs), the army doesn't have any sort of blanket immunity to morale. They are still Ld10, but obviously we know that still leaves them very vulnerable to being run down in combat, and it looks like that will remain a big Achilles heel.
20) Scarabs sound great. They are cheap, have the new WBB rule, move like beasts and have an ability that erodes enemy armor when they get into combat with it. Any non-vehicle model they wound, but don't kill, has its armor save turned to a dash (i.e. nothing) for the rest of the game. If they hit a vehicle, on a 4+ the vehicle loses a point of armor value on ALL facings, and if any facing is reduced to zero, then the vehicle is destroyed (I'm not sure if this ability kicks in for each hit they get on the vehicle, or just once no matter how many hits they cause). There are some items in the army that also have a similar ability to erode armor, including one of the C'Tan powers.
So it sounds like Scarabs may play a major role in most Necron armies!
21) Overall, CC is definitely still the weak point of the army, but it looks like they've got a lot of different places they can take special rules to slow down or screw with approaching enemy, including some of the C'Tan powers, but also some of the different gear they can take. But they also have some different potential counter-assault units, which mainly come out of the Elites section (besides the new Walker, the C'Tan and the flayed ones in Elites there are 3 OTHER brand new units in there as well, for a grand total of 6 Elites choices). The Flayed ones are, being consistent, cheaper than they were and now have 3 Attacks base (but their save is now 4+ as with standard Warriors). One of the other new Elite units is also CC oriented, but is very pricey points wise (but is S5/T5/3+save). This unit can wield a Warscythe, but they are not called Pariahs (no idea if that's what Pariahs have 'turned into' or not).
Another new Elites choice is a sniper style unit that can Deep Strike into play normally or it can choose to immediately Deep Strike immediately after the opponent brings an enemy unit on from Reserves, and they have some nasty additional damage ability against one nominated unit...obviously we need more info to know how useful this will really be, but the concept of countering an opponent's Reserve deployment immediately sounds interesting at least.
The last new Elites choice is an Elite Jump Infantry unit with very close range shooting and some decent CC ability (and are also S5/T5/3+save).
22) Fast Attack has 4 choices...Wraiths, Tomb Blades (jetbikes), Scarabs & Destroyers.
And that's it! Kind of all over the place and certainly not a full snapshot of the codex, but a lot of these things are completely opposite from many of the other rumors I've seen out there.
New Necron Rumors Are On The Rise
Here is the latest round of rumors from Dakka Dakka -