I'm just back from my first game with 5th Edition Necrons (or should I say 6th Edition?), and I'm totally convinced that this is a fun army to play.
The game was 6000 points each side, Necrons took on Grey Knights, Space Marines and Chaos Space Marines in an Annihilate mission. I don't think a single turn went by without some special rule or another ruining our opponents' plans, and by the end of turn 4 the Necrons were ahead 14 kill points to 7.
Because all three of us with Necron armies were building on forces we already had there was in excess of 100 Necron Warriors on the table. I was the only one to put Crypteks (or any Royal Court members, for that matter) into mine, but was glad of it. The combination of Transmogrification Crypteks and a Writhing Worldscape C'tan is absolutely phenomenal. I spent a good part of the game taking pot-shots at a unit of 20 Khorne Bezerkers, killing a couple of guys to dangerous terrain each turn, and even took a wound off of Abaddon when his unit of Terminators was forced to test.
One of the Necron armys included Imotekh, and his night fighting rule meant we could engage the enemy right at the range we wanted. The extra chances for lightning strikes in a game this size helped out too!
Most Necron units are still vulnerable to combat though, as you would expect. I managed to avoid this for the most part, but several squads of Warriors further down the table were removed in the assault phases. Fortunately the new codex has tricks and units that meant we were almost always in a position to offer some kind of counter-attack in our own turn, typically wiping out the offending unit.
And let's talk about Deathmarks briefly. Mine spent the first few turns hanging back, as I didn't want to be over-eager and throw them away just for one round of shooting. Instead they waited until the enemy reached our line, then combined Veil of Darkness, Hunters from Hyperspace, and some rending that I was reminded of to really tear into a unit of Terminators. The next turn they were able to use the same trick to warp half way across the field and hit a different terminator unit.