I mentioned offhandedly that I took the Nightbringer out of my 1500 point Necron army in lieu of a Monoloth in a post last night and some people have asked why so I thought I'd break it down for you guys. For the record, I'm not totally for or against either of the C'tan in any sized army, if you can make it work, more power to you. This is just why I, personally, chose not to.
Most people put the Nightbringer (or Deceiver) in their armies because either they think the model looks really freaking sweet or that just from reading the codex, he sounds really overpowered. Well, they are gods, technically. And although the idea of having a really overpowered god running around the battlefield destroying everything is really appealing, I've found that in practice, it doesn't really work out that well in a small/medium-sized army.
One of my biggest problems with the Nightbringer is that C'tan can not attach themselves to friendly units because of Above All Others. This is a problem for Necrons because one of their blaring weaknesses is being pretty weak units in melee. So I want an army of units that support each other so that I can take the minimal amount of losses, and the Nightbringer offers pretty much no bonuses whatsoever to the rest of the army. On the same note, his attacks, like Gaze of Death, don't discern between friendly and enemy units. My 1500 point army list has two basic parts: sacrificial units that go into melee as tar pits or distractions, and then the large majority, which is strong ranged units that I want to keep from ever seeing close combat as they pick off everything else. So obviously, I want to get those melee tar pits out there to tie down enemy units as fast as possible. This brings up a second point, being that the Nightbringer, although capable of functioning as a tar pit, is SLOW. He's really easy to avoid getting into CC with completely, and although he has decent ranged attacks, you basically end up with a really expensive single unit running around the table trying to chase down things and making itself a huge target to be singled out and picked off. It's possible to send a unit of Scarab Swarms ahead of the Nightbringer to hold enemies in CC while he catches up, but I find a cheaper alternative is to attach the Swarms to a Destroyer Lord with a Lightning Field, which moves a lot faster, and can be just as annoying.
This leads to my primary argument against the Nightbringer in a 1500 army, which is Phase Out. Most people in friendly games will agree to not use the Phase Out rule since it's outdated, but it's still a totally valid tactic, and if you're in a tournament, you can darn well bet your bottom dollar the opponent's going to use every advantage he has against you, ESPECIALLY Phase Out. So when you play Necrons competitively every point is precious because you want to make sure you don't end up with too few Necron type units and that you keep as many of them alive as you can. That being said, the Nightbringer is REALLY EXPENSIVE. He's 360 points, that's the price of 20 Warriors or 7 Destroyers.
My alternative to the Nightbringer is the Monolith. A Monolith costs 235 points, which is still a big chunk, but it is infinitely more versatile. Monoliths can function just as well as a distraction as a Nightbringer, are twice as tough, and provide amazing support for the rest of the army with the abilities to teleport units out of CC and provide cover if necessary. It still moves really slow, and can be just as easily ignored, but it can do a lot more ranged damage than the Nightbringer, so it doesn't really need to get into melee, but if it does, the Monolith is arguably the hardest thing in the game to kill.
Here's an article that elaborates more on the Nightbringer's pro's and con's. As for just plain Necron tactics, I think this guy is a lot better at explaining than I am. Again, I must give props to Paul, he sends me a lot of these links that I post and helped me sort out a lot of bugs in my army. One of the best things to do when building an army is talk about it to someone else who plays the game and knows the rules, it's always good to get a second perspective.
So speaking of second perspectives, I'd like to hear your opinions. 1500 point army, Nightbringer or Monolith?