So after a few games played, a few watched and much, much list building I have some thoughts on the new codex. In no particular order...
Please note these are just my thoughts, you may not agree with them but I wish to promote a good discussion.
Also note, despite me pointing out a lot of thing I believe are bad/could be better, I do enjoy this codex. It will still provide a good challenge to use and as a player o the old necrons, I enjoy this codex.
The ranged anti-tank is extremely limited and unreliable, where there is reliable anti-tank it is either far too costly or too easy to kill (or both).
Anti-Infantry fire power can be found in droves.
Quantum shield rarely comes into play, once that vehicle is penetrated the chances are it is going to die before being reduced to AV11.
Annihilation Barges 'should be' fast to be usable, or at least the destructor needs o be 36" range. It is very easy for an enemy to avoid.
The Doomsday Ark is too expensive for what it is capable of. The AP1 points to a tank hunter, but the gun is not ordnance, nor is it S10, the move and fire rule becomes a massive liability from turn 2 on wards.
Killing Terminators is still extremely difficult, there are units that will do it, but they are generally over priced.
I have a feeling Tremor Crons (Tremor Staves + Orikan + worldscape) will be a common build out of this codex. It is effective (Orikan not required...) and gives you a lot more shooting time.
Some of the better weapons suffer due to AP-, and to swap them out for a weapon with an AP costs you strength.
If you don't base your list solely on Gauss, it becomes very limited.
Doomscythes have potential, but not having quantum shielding is the real ball breaker. Their cost is also considerably high when compared to other unit of similar ability (Ravager, Vendetta etc).
Deathmarks are a solid choice, however expensive.
The Special Characters all lack something, weather it be a res orb, phaeron or an Invul. All of them are missing 1 thing that would make hem far more worth while. Such as Trazyn not being a phaeron, or Imotek not having a Res-Orb. The Cryptek character not being able to take a unit of crypteks seems very out of place too.
Command Barges, if they live, are insanely good with a Warscythe lord in them.
Triarch stalkers, whilst slightly over costed are a solid choice.
Scarabs are easy for an opponent to avoid. Their main ability to kill tanks can be nullified easy with some infantry (generally loosing combat against MEQ and not doing much other wise) or by moving the tank they will go after over 6". I am almost considering not using them simply because a competent opponent will make them next to useless.
Wraiths are reasonable, but to make them so they require whip coils. They cannot take on Dedicated Assasult units reliably but are fantastic for taking out objective sitting units like scouts or other weakened scoring units. They are also very good for killing lone characters.
All units pay out the ass for Reanimation, but it makes little difference I have found so far, since your army is generally lower on number than the average marine army, 1/3 models is not a large amount.
The available combos are powerful, but are either very expensive or very hard to maintain.
Taking any additional support (crypteks, lords) for units, beco0mes very expensive very quickly. 65 point to get a res-orb on the table minimum is quite possibly too much considering they now only support the unit they are in.
All of the fun wargear (Arrow, Labrynth etc) costs far too much considering how situational it is or the chance that it won't do anything.
Monoliths are a reasonable choice. Though their reliance on getting close with their lack of the old Living Metal rule is a liability.
C'tan are quite useful, but possibly over priced for their stat line. Some of the costing on their abilities seem oddly priced as well.
Many rules are 'overwritten' to the point of abiguity. Some of the issues, I hope the FAQ will clear up without making the codex worse, but actually more useful in some areas (what am I saying, its a xenos dex...).
Overall, I feel the codex will go the way of the Tyranids. Many people will pick it up for a brief period and than realise it is difficult to make work, going back to their other army of choice with a few dedicated players keeping with the codex.