It was actually the Nessian warhounds that caused us to have a character die, as far as I could tell. The area effect of the breath weapons just stack up with each other, because the things in the third row back still hit you with fire. I thought the challenge level was great, and if anything, perhaps a little lighter than I would have liked to see, given we were still able to make headway with one warrior and two casters. But no, the XP was definitely not consumate to the risk. And yes, greater variety would have made things more interesting.
If you ask me, you wouldn't have to go hog wild mixing things up on the variety side. All you'd really have to do is sprinkle in, say, one caster that throws dispels from the back of a pack of hounds. Then three fights later, some fighter type humanoid-ish thing with, say, the same AB and AC as the revenants, but four times the HP, but only one of them. Then four fights later, a pair of sneak attacking revenants that come at the party through the walls from behind, with just enough AB and sneak attack damage to get your attention, but not overwhelming. As in, just sprinkle in some little touches, as opposed to making it a dungeon with three more monster types that appear all over.
