I really like what they did with the Destroyers. Being able to mix in the heavies with them and moving to fast attack really is nice. Although I dislike the nerfs to the unit, I have to say this is a good unit for putting the hurt on MEQs unfortunate enough to have left their vehicles. For how "shooty" this army is going to be, I don't see them being a big priority for the enemy either. Park them behind some terrain and wait, IMO.
As for the Wraiths, they look great but once again the low initiative really gets me. I understand the Necrons are not a CC army, but that doesn't mean we don't have a few elite-type units who do specialize in it.
As for the Scarabs.....I don't think I will be able to send enough of these at my enemies tanks! These little buggers would scare the hell out of me if I were Marines. What do you do? You can blow all your heavy fire into them if you want...that just keeps the fire off my Doomsday Arcs! Or you can ignore them knowing your AV14 will turn into a Rhino real fast. These things are probably the sole reason, after reading the codex, that I am going to stay playing the Necrons. I am not overly impressed with 90% of the units in the codex, but when adding these things into the mix, I can see the light at the end of the tunnel.