I'm totally fine with them being "Tomb Kings in space," for the simple reason that they were freaking boring before. Yes they are cool-looking, mysterious death machines, but when I'm painting the 12th gunmetal-grey skeleton in a row, I start to wonder whether I've gone a little wrong. It's possible to give them a modicum of personality without diluting their general air of horror and enigma. For instance, Necron Lords having different forms, and basic personalities. I mean, there are only 2 C'Tan active in the galaxy, and potentially millions of tomb worlds, so it makes sense that these Lords would be made to have a little initiative and autonomy.
I've probably said this before, but characters and factions are only interesting if they have flaws. Necrons have mostly been built up to be a completely unstoppable menace, able to appear anywhere they like, unable to to be killed (they'll either self-repair or phase out), and possessing technology such that the basic grunt weapon can vaporize a Space Marine. Your fancy, god-like psychic powers can't help you, since the Necs invented an anti-psyker gene, and they're led by the physical manifestations of star gods.
The way it's shaping up now, the Necrons have certain disadvantages. Some of their tombs have decayed, or been lost. As a Necron is repaired more and more, it become gradually less useful. Some Lords have gone insane. The C'Tan can't be everywhere at once. It's these kinds of things that add flavor to them, that make me interested, beyond "they're mindless, omnicidal robots." Which is a cool concept, sure, but an equally cool one is legions of robots, sealed with the population of a long-ago-empire, returning to life beneath our very feet to destroy the hated living, take back what's theirs, and enslave the universe in the name of their twisted gods.