I was invited to tank Vet Graven Deep last night. It was my first time in the dungeon but we blew through it all the way up to the final boss. Before I say more on that, let me tell you how beautiful and engrossing this dungeon is. I love the haunting atmosphere that is juxtaposed with the beauty of the ocean depths. I found myself stopping to admire it all and I don't think I've ever done that in a dungeon before. It's masterfully done.
Now, about the encounters and the imbalance in difficulty: The trash mobs and secret bosses were way too easy. We questioned whether we were on vet or not. But then we got to the final boss and there was an EXTREME increase in difficulty. It was so hard that it felt like we were doing hard mode. I think it's every bit as difficult as Fang Lair hard mode. There's no way normal vet should be that difficult. I had to leave to go to bed at 2:00 am. I don't know if the others were able to complete it without me. Still, I can handle some vet hard modes and that's what it felt like.
So overall, it's an very well done dungeon that unfortunately suffers from some imbalance in difficulty.