The problem is that Dark Eldar are a thinker's army to play, but playing against them is not so much. Anything with a flamer template is pretty much a hard counter to most DE units. Basic bolters can shoot down out vehicles and planes (especially since the bomber dropped in armor while going up in price). IG Wyverns do such horrible things to the army that going up against them is practically a NPE. Add to that per the rumors, a lot of the "thinking tools" are gone. Haywire wyches to take on vehicles, bladevanes letting us maneuver and deal wounds instead of braving overwatch and getting stuck in, wych weapons letting you use careful unit positioning to minimize enemy attacks with shardnets, all seem to be gone.
I'm usually quite positive (though some people seem to think that being positive about GW seems to be a crime) and quite enjoy the GK book, but from the rumors, this DE book is highly disappointing- it doesn't seem to fix the basic problems of the army, in that the lack of durability is still too high for the damage output they can generate. Reaver jetbikes lost their ability to dance around doing damage while avoiding being tied up in combat, meanwhile the Light Eldar keep their basic troop jetbikes that somehow grant power armor to the wearer.