Well, Ulduar is obviously a lot, lot more interesting than the level 80 version of Naxxramas. The content is just vastly bigger than the one at the beginning of the Wrath. The challenge of the bosses is higher as well, getting to Yogg-Saron is nowhere as close to as beating Malygos or Kel'Thuzad.
While the harder and more interesting content is also harder to access, I just think that's just a good thing. The "nerfs" flying on and about the instance is something that worries me - I hope they don't go too far away with the casuals, even though the nerfs on the FIRST bosses of the instance are justified. I don't think the entrance level should be as hard as Razorscale was, specially in non-hardmode versions. (You shouldn't even mention pre-nerf Ignis compared to Razorscale and XT002, because it was a lot harder than those two encounters... in the end in my opinion harder than Mimiron as well.)
Well, Oblivion now took their first step into the Descent of Madness, reaching down into the ruined prison of Yogg-Saron after killing Vezax. First pull without tactics on Yogg-Saron was hilarious.