I've been reading the new rulebook all day and the new FAQs have come out. From what I've seen so far necrons have gained a lot more than they've lost.
My not exhaustive list of awesome new things:
• Command barges are now chariots and can charge into combat! The lord on board can also negate the loss of armour points.
• Wraiths whip coils now work properly against grey knights force halberds.
• Wraiths also get an extra I10 strike in combat when charging.
• Spyders now have as good a psychic defence as psychic hoods.
• Spyders and C'Tan cause Fear! Omg awesome.
• Spyders get an I10 hit when charging!
• Fearless models now don't take fearless saves when loosing combat. Scarabs, wraiths and spyders just got an amazing boost.
• Night fight change. I'm not sure if this is better or worse for Imotekh armies.
• Warscythes are back to being one of the most awesome weapons in te game. They have AP1, armourbane and don't get an initiative modifier like most weapons that add strength now.
• The changes to rapid fire make warriors awesome and their ability to strip armour points is awesome too.
• Scarabs don't have stealth anymore :( they still have 'vulnerable to blasts' and now they ignore difficult terrain.
• Our skimmers now have 'jink' saves. I.e. if the skimmer moves it gains a 5+ cover save. If it goes flat out it gets a 4+ cover save.
I'll update this list when I notice anything else. My brain is busy melting at the moment from all the new info.