I've discovered that I'm a bit of a "theme" player. I build my armies around an idea, and enjoy playing out that idea on the table-top.
When I started my Tyranid force, I was just learning how to play. I spent some time on The Hive Mind forum, read Loate's unit tactica (which I post to every thread I ever read for new Tyranid players) and bought a force. As I've expanded that force, it's grown around an organically occurring theme--that of a Hive Fleet falling upon an enemy position in wave after wave of bodies. I have a fast flying wave (Gargoyles and a Flyrant), a fast ground wave (Hormagaunts, a trygon, and my favorite: Raveners) and a slow advance (Hive Guard, a walking Tyrant, tervigon and accompanying termagant screen--Tyrannofexen when the model is released). In a perfect battle for me, this army crashes upon an enemy like an advancing tide.
When Dark Eldar came out last year, I gleefully jumped the bandwagon. This time, I chose a theme deliberately--that of a lightning fast mech force, focusing almost entirely on shooting, with the exception of my Archon and her Incubi retinue. I consciously tailored my force to play completely differently than my tyranids. I wanted a change of pace, after all, so beasts and monstrous creatures really weren't worth it to me--I have more fun ones in my tyranid collection, after all! In time, I plan to expand the Coven of my force beyond the generous gift of a Talos and some Scourges one of my friends was kind enough to give to me, but not for a while, I think. My resources must be husbanded carefully, after all!
This leads me to why I'm writing this in the first place. The other day, I posted about whether I wanted to start Grey Knights or Necrons. This got me thinking about what kind of army I wanted to play next. And I can't seem to figure out what sort of army the Necrons are. That's why I'm having difficulty getting as excited about the Necrons as I had originally. Because the models are GREAT, and I want them, but I don't know how they synthesize into an idealistic whole. A Grey Knight Paladin force with a slight inquisitorial element (two models, despoiling my purity...) has a theme I can sink my teeth into. It's a rock, pure and simple, and you just let the guy across the table deal with it while you go to town.
Would it be hard to beat? Hell no. My Dark Eldar would be laughing their butts off all the way to Commoragh with Draigo's head on a pike after a game with my putative list*. But it would be fun to play, cool to model, and it would look pretty good, I hope. And it would be significantly different from what I already play (Super-fast shooting and swarms with big bugs).
I can't figure out a pull for the Necrons. They have a range of great models which I want to possess, but I'm just not sure how to synthesize them at this stage. Maybe once the Codex comes out, the clouds will open and all will be made clear. But right now, I'm just a wee bit confused.
*For those interested, it consists of Draigo, two units of 10 paladins, an Inquisitor, and a Vindicare. Just over $250 at GW's retail price for a 2000 point list.