After Nihilum "finished" Naxxramas 3 days after Wrath of the Lich King came out, there was some discussion of whether raiding was too easy. But then there was a long silence, and while some other top raiding guilds repeated the feat, the majority of players hasn't even seen Naxxramas yet. My guild did their first raid last Friday, before I was level 80, so I didn't even sign up. And on that first trip they killed one boss (Patchwerk), and got the second boss (Grobbulus) of that part of Naxx to 25%. Which, in my opinion, is quite reasonable. Kill the first boss on the first trip, but don't immediately have the place on farm.
So from this and similar anecdotal evidence it seems that Naxxramas is well enough balanced. A typical raiding guild (not the ultra-leet) will find the encounters challenging, without them being frustrating.
So, how far are you in the "new raiding"? Visited Naxxramas yet? Found it too easy, just right, or too hard? Would you say that, provided Blizzard adds some much harder raid dungeons to the game afterwards, Naxxramas is at the right difficulty level for an "entry level raid dungeon"?