Same old stuff with a new paint job
Some of the mobs are wearing the same skins as those from level 60 or 70. I was fighting this one mob in Hyjal and he had the merciless gladiator's warlock helm on (season 2 I think).
They also had these charbringer mobs I believe which were basically reskinned mobs from Molten Core. I can't remember what boss it was. Might have been Majordomo or Lucifron. I forget.
Anyways, I wouldn't really consider Cataclysm an expansion because they pretty much recycled everything. So far at least. I am only level 81.
I heard it's nice that people will have to CC in instances again instead of just plowing through them with WOTLK. So they'll actually have to work for their rewards.