I have so far tryed four different instances, The nexus, Utgaard Keep, Azjol-Nerub og Drak'Tharon Keep.
Just a few facts, the instances is in lenght like Ramparts is in TBC. They are very compact and with 3-4 bosses in each. They aint long runs with alot of thrash. And there hasent so far been any really tricky thrash or pulls. Not alot of tactics on em, more or less just tank and spank. Some bosses are tank and spank, some requires some tactics. And some which I will go a bit further into, have a little extra up there sleeve. The endbosses in Drak'Tharon Keep and Azjol-Nerub, they are another more thing among alot of the new stuff that raises the game to higher levels.
The one in the Keep, presents you with 2 phases. One normal tank and spank phase, and one skeleton phase. The skeleton phase makes a new side of the game. You all get turned into skeletons, and you get, like when you enter a Siege weapon a new bar with speciel skeleton abilities. It makes it more hectic, and force the players to be a bit more switched on. One thing I really like.
The one in Azjol, is a creature which goes up and down into the earth. When he is down, he spawns adds you have to deal with. That recipe is seen before and have nothing new in it. But the way the adds come and the boss gets under/over earth, made the whole fight fast paced and fun.
I guess those 2 fights gives a good picture of how the instances seem to shape. A short run, with alot of speed and action. Packed with great monsters and bosses and some small twist's. I really think they have stepped up here. I enjoy it all alot. Im the only one thinking Diablo when I write that.
My own paladin is now almost level 77, and atm questing in Zul'Drak. Last zone was Grizzly Hills, a great forest area, with alot of good quest chains. Zul'Drak is a cool place, its really evil and destroyed in its look, and there is more or less obscure creaters everywhere. With small outpost of Argent Dawn, fighting everywhere. It really have an feel, as a zone in constant war. And I can promises you that it is.. :)
Just did the new "Ring of Blood", which is located in Zul'Drak in this expansion. You get to fight some cool bosses, especially a fire guy. And the last boss it worth seeing. The last boss is riding a big mammut. After 15-20% into the fight he jumps down from the mammut, the tank then jumps on the mammut and tank the boss from the back of the mammut. Cool twist once again. A event you should not miss out on.
Time to get back to questing, catch you at 80.. ;)