ZG seems like a pretty good new instance to me, new boss mechanics, new trash mechanics with beautiful nostlagic ambience and the beautiful troll environment. Before you critics jump straight into denouncing Blizzard for the implementation of these dungeons, maybe you should consider running them or at least watching some of the boss fights:
ZA has just been released on PTR too, so i can't wait to see what new bosses or mechanics are released.
To those who commented that Blizzard are only implementing 2 new heroics blah blah, Firelands is a new raid dungeon coming out too in 4.1 with also the possibility of a new underwater instance as stated at Blizzcon. Also keep in mind this quote
We have more in store even past patch 4.1 and we'll be sharing more details about them before much longer. We'll also be sharing a more complete look at Zul'Gurub and Zul'Aman (including the updated mounts.) Though, testing on the PTR will get you a look at it more up front and personal.
We are not near the "end" of things in World of Warcraft nor at the "end" of our ideas. Development takes time though and we plan to make sure that experiences in game continue to be epic.
I also can't find the blue post regarding how Hyjal will be refurbished this patch; remade back to it's glory, after our questing saved Hyjal from being destroyed by the Twilight Cult, including new daily quests etc. This seems amazing from a lore/storytelling point of view in which many disgruntled posters have been using as justification in disparaging the implementation of ZA and ZG.