The Dark Elves have a nice selection of infantry units there. Sword Infantry aside Spear Infantry unlike the High Elves who just have spears. It'll be neat to see the Darkshard (Repeater Crossbows) in action, and them being able to have shields is a nice advantage over the High Elf archers, probably to compensate for shorter range.
Apparently the Cold One Dread Knights have maces. I'm guessing that means they'll have armour piercing attacks. A bit odd to me that Shades can have great weapons but I don't know much about the Dark Elf army list.
Some more details are gathered here, in a Reddit post.As an army the Dark Elves will have an ability called "Murderous Prowess". When casualties increase (Yours or the enemies) to a point all of your units will gain a large buff to their combat stats for about a minute. The amount of casualties required will change depending on the size of the battle. Witch Elves have "Murderous Mastery" which gives them an even bigger buff from "Murderous Prowess".
The Cauldron of Blood seems like it has abilities that can give your units things like rampage and melee buffs.
Assassin has different poisons, including one that can get through city gates quickly.
Witch Elves have a poison that causes rampage. I think this means if you attack an enemy unit with it they'll force attack.
War Hydra breathes fire and has an improved version of regeneration.
Black Dragon has noxious breath with a poison debuff that lasts long enough to use the breath attack again before it's over.
Missile Dark Riders and Cold One Chariot both have repeater crossbows. Apparently repeater crossbows are armour piercing but the Dark Riders can't fire while moving and the Cold One Chariot can rampage.