Some musings on the rule changes and new units in the new codex:
First of all, the army no longer fades once it's down to less than 25%. Also, Necrons only repair themselves on a 5+ now (can be increased to 4+ with a Resurrection Orb), but it works against every sort of attack. And (almost) everyone does it now.
Necron Warriors are now weaker and cheaper. They only cost 13 points, but only have a 4+ armor save now.
Immortals are now Troops. Their Gauss Blaster is no longer an Assault weapon, but it's still a S5 AP4 weapon on a Marine-profile for 17 points. They can also carry Tesla Carbines which trade the AP for the ability to score 2 additional hits and ARE assault weapons.
Warriors can take a Ghost ark - an open-topped skimmer that can resurrect destroyed Necron Warriors at any time and is quite resilient for a transport vessel (13 armor on front and sides until it gets a penetrating hit, after which it has 11 on all sides).
Both Troop choices and several Elite choices can take Night Scythes as dedicated transports. Those are fast skimmers with 11 armor that can transport up to 15 models, can fire all their weapons at cruising speed and move 36 inches when going all-out and are armed with 2 S7 Assault 4 weapons that can hit more than one unit. At just 100 points they are a steal, but if they are shot down the transported unit will go into reserve and can't deep-strike.
Deathmarks are a unit of Snipers (their rifles target brain-tissue and are rapid-fire weapons) that can arrive via deep-strike immediately when an enemy does the same. And they will wound a single unit you can designate on 2+.
Lychguards are the new Immortals - Bodyguards for your character models. They have Strenght and Toughness 5 and two attacks and carry Warscyhtes - two-handed power weapons that give +2 strenght and 2D6 armor penetration. Those can be upgraded to normal energy weapons and Dispersion shields - the latter give them a 4+ invulnerable save, and if they pass it against a ranged attack they can deflect it upon an enemy up to 6 inch away. However, they are pretty expensive at 40 points per model (45 when upgraded).
Triarch Preatorians are S5 T5 jump infantry with S5 AP2 assault 1 weapons - that have just 6 inch range, but double as power weapons. They can also be equipped with the more conventional pistol&sword, the former being S6 and the latter a power weapon. Again very expensive at 40 points per model.
C'tan now come as "Shards" in the form of monstrous Elite units that can be equipped with a range of abilities too wide to cover here.
Flayed ones can now deep strike and infiltrate, have 3 attacks per model and cost just 13 points. However they only have a 4+ armor save.
Triarch Stalkers are walkers that can be equipped with a variety of nasty ranged weapons. They also have 13 armor (until penetrated), but are open-topped and lack cyborg-melee weapons. Their 150+ point cost and Elite status can be justified by their special ability - if they hit an enemy all attacks against that unit count as twin-linked for the rest of the turn.
Canopthek Wraiths are an upgraded version of the old Wraiths. Oh, and now they can be equipped with a short-ranged weapon that insta-kills without save if the enemy fails a strenght-test.
Scarabs now profit from a new Necron special rule (that is also found on a few weapons) that allows them to permanently remove a models armor save or reduce the armor on vehicles.
Tomb Blades are small Necron space fighters - they function as Jetbitkes. As such they have toughness 5, but only a 4+ armor save unless upgraded. They can use a variety of ranged weapons, and are not too expensive at 20 points before upgrades.
Destroyers are pretty much the same as before, except that they are now Jump Infantry - and are now one unit type, with Heavy Destroyers being a weapon upgrade and both being mixable in the same unit. That also makes Heavy Destroyers a Fast Attack choice.
The Monolith can now use it's portal to force all enemy models within D6 inches to pass a strength test or be removed without save, in addition to it's teleport function. Note that living metal has been changed and now only prevents crew shaken and stunned results (and not always, depening on a dice roll) - however, all vehicles have it. The Monolith now costs 200 points.
The Doomsday Arc is armed with a Strenght 9 AP 1 large blast weapon with 72 inch range. However, if it moves the weapon is much weaker (S7 AP 4, 24 inches small blast). It can also fire broadsides of 5 gauss flayers at seperate targets (and shares that ability with the Ghost Arc). It costs 175 points.
The Annihilation Barge comes with 2 good, medium-ranged weapons and is much cheaper at 90 points.
The Doom Scythe is a Night Scythe that exchanges it's transport capacity for a Death Ray - it hits every model along a 3D6 inch long line with S10 and AP1. It's much more expensive than the Night Scythe at 175 points.
Canopthek Spyders are monstrous creatures that can repair vehicles, produce Scarab Swarms and nullify psychic powers within a short range.
HQ-choices are pretty basic - just two in addition to the special characters.
A Necron Overlord is pretty much the same as the old Necron Lord. He can now ride a Command Barge - a fast skimmer that allows him to make attacks from within if it moves over units and which he can repair by sacrificing wounds.
If you take an Overlord you can also take up to 5 Lords and up to 5 Crypekts. Both can be split off into an Infantry unit. The Lords have 2 attacks, Strenght and Toughness 5 at 35 points each - they can act as Sergeants can of course put Resurrection Orbs (which now only work on a single unit) into your units. Crypteks are no better than Necron Warriors, but can put a lot of fancy equipment that was formerly carried by Necron Lords on the Table, such as the Veil of Darkness or the Solar Pulse. Each special equipment can only be taken once, preventing extra-strong cheese quite well.
Destructor Lords have the profile of a Necron lord with 6 Toughness and act as jump infantry, but don't allow you to take lesser lords or Crypteks.
SoS:NBA GALE Force
"Destiny and fate are for those too weak to forge their own futures. Where we are 'supposed' to be is irrelevent." - Sir Nitram
"The world owes you nothing but painful lessons" - CaptainChewbacca
"The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one." - Wilhelm Stekel
"In 1969 it was easier to send a man to the Moon than to have the public accept a homosexual" - Broomstick