No they aren't. They're too loving slow, I've never lost a 1v1 against Necron because they take like 5 minutes to get anything hardhitting out.
And all their stuff moves at a crawl.
My friend brought DoW over once and I started a Necron campaign thinking "oh sweet, egyptian zombie robots this is gonna be awesome"
Half of each level was spent waiting for the forgeters to shamble across the map.