1. Asdrubal vect: Expensive (supposed to be about the same cost amount as Mephi), but for his ability to allow the army to steal the initiative on a 4+ he is worth it in my eyes... Especially since he will most likely be able to do a lot more than just allow good roll.
2. Archons, sound like they are going to be able to be nasty little people. I imagine they will have stuff that will make any CC unit scared to engage them. The only problem I see with them is that they are still in a nice squishy AV 10 open topped transport. The Archon can supposedly be picked out in CC, which means watch out for fists, relic blades and the such.
3. Flyers, flyers, flyers... I can't believe all the flyers coming into the game these days. With the ability to purchase missles, I can see the Dark Eldar missle Alpha Strike to be a nasty one... Not only that but they can move a bunch and still fire their st 9 lances. look out guard, someone is on your flank!
Over all, I feel that the DE are fleshing out from the previews and rumours to be a big time glass cannon.
For example, Take vect and win the roll to go first. Opt to go second and watch your opponent curse when you roll that 4+ to seize. With all his armor positioned for first turn rush/alpha strike as many armies will there won't be much taking advantage of cover. This will allow you to best deploy to shoot flanks (becuase you chose to go second) and go first. Essentially giving the alpha strike to those who intended to give it to you.
Some people have been saying that the lance ability isn't that powerful because of razorback spams popularity, but remember that even though it doesn't use the AV 12 ability, it is still st 8 (and in some cases st 9)
In short: As I said earlier, Dark Eldar seem at first glance to be a very momentum based glass cannon army. If you take their momentum from them you will watch them crumble.