I'm in the middle of the necron campaign, and I have to say, they're absolute gutter trash.
For starters, the weaponry on Escorts and light cruisers has as much firepower as throwing rocks. Which, in itself, isn't all that bad. but when you consider necron ships are slow, unshielded and pricy, it becomes laughably broken.
but my worst issue with necrons is their absolutely abysmal pathfinding. My ships are constatly running into each other, they constantly just bumble into one another when getting into firing position. I know this is a strategy game, but this is a problem I have with absolutely no other faction. Do you honestly expect me to have to hold the hand of every single ship?
so, to sum it up, garbage AI, terrible weaponry, no sense of direction... need I remind everyone these are supposed to be Necrons? The scourge of the Galaxy? or did they just trip and bumble their way into Galactic dominion?
although I will admit that the Economy in the necron campaign is MUCH better than it is in the Imperial Campaign. you should add that to the list of things to switch over.