As raiding has progressed in Northrend, a lot of players have made the comparison between Naxxramas and Karazhan. The general wisdom is that Naxxramas is an introductory raid, like Karazhan was, and so it is OK for it to be easy.
Of course, those of us who were raiding earlier in Burning Crusade recall that Karazhan was not easy at all. In the first months of BC, Karazhan was a relatively slow progression for many guilds – especially the more casual guilds. Moroes was a roadblock for many guilds for weeks. You often saw guild runs, and later pugs, that would only do lower Kara. It wasn’t until later in BC that pugs were regularly doing full clears and people did speed runs in Kara.
So, I don’t think that Kara and Naxx compare well. On my first 10-man Naxx run I made it through half the instance with few wipes. Naxx is comparatively much easier.
Ulduar right now feels like Karazhan used to. A lot of guilds have had to work hard to get Ignis down. Deconstructor is a gear check, much like Curator was in Karazhan. A week when your guild gets one new boss down is considered an accomplishment. Some guilds and pugs can go into Ulduar and get Flame Leviathan, Razorscale, and Deconstructor, and maybe Kologarm but then get stuck.
The whole raiding atmosphere in Ulduar reminds me of Karazhan. My guild took months and months to finally clear Kara. We had weeks of good progression, and weeks where we backslid. Downing a new boss was exciting. I expect Ulduar to be the same. I hope that my guild members have the patience for it, because Naxx has set a certain expectation for boss kills and loot that we won’t experience in Ulduar.