I've got one thing to say, might not be really about the new instance, but I saw that the new instance mobs have the same amount of health and do less damage than the Stratholme mobs, not even saying anything about the next two, so you might want to Nerf the instances from VI to VIII gear.
Other thing I'd like to see would be that the bosses could drop one or two fun items with a low chance, he'll maybe a mount with a very low chance (i.e turtle mount :?).
I like the new instance a lot, 10/10 IGN. I like the patrolling mobs and the spell that the mobs have, tho I'd like to see the hellcallers do a bit more damage with the shadow bolt, in rest I like the bosses, the location and the size of the instance.
Keep up the good work.