Collected from the 'net.


--Zul'Aman will be a 10-person raid zone
--Zul'Aman will be on a quicker reset than 7 days (some might call this "casual")
--Zul'Aman will be MORE difficult than Karazhan and drop better loot (some might call this hardcore)
--Zul'Aman will feature 6 bosses and it's our goal that you can kill them all in one night -- perhaps 2-3 hour clear times (some might call this casual)
--Zul'Aman will not have a key requirement. Nor will it have an attunement quest\ (some might call this casual)
--Zul'Aman will have a VERY challenging timed quest for those who choose to participate in it. This *will be* hardcore and will be very rewarding. Players do not have to engage in the timed run (very similar to the Baron run in Stratholme)
--We're tuning the first boss in Zul'Aman to require less raid coordination than some other raid bosses. He will still hit very hard so you'll need to be geared properly but it won't take 15 minutes to explain the fight. It will be a simple yet challenging fight. The other boss fights get more complex and challenging from there. If players want a basis of comparison, imagine the tuning of ZA started around Nightbane/Prince difficulty and ramped up from there.

ZA is a very cool looking zone. It will feature brand new troll models -- Forest Trolls. They are very impressive looking. There will also be a large amount of brand new item art in the zone. We'll get screenshots of this out soon.
I know this question is going to come up so I'll answer it now --
Yes, you can totally skip Karazhan if you're an amazingly elite guild who doesn't have time to key up for KZ yet can face the challenges of ZA without gearing up in KZ. Have fun storming the castle.