This is the biggest problem of Wrath of the Lich King.
Let's look at The burning Crsuade-expansion for a moment. When this was started in Januar 2007 the following Raids were included:
Tempest Keep : The Eye
The Battle for Mount Hyjal
Doom Lord Kazzak
..that Fel Reaver outside Black Temple
That is a lot of content, maybe to many, but at least there was something after the Karazhan. Now Karazhan was hard, not only did you have to do a long quest-chain that took you through several heroics (and you needed to be exalted with the faction those days to do heroics), it was also hard even if you had the best non-raid gear on you.
So Blizzards descision to make Naxxramas an entry-level-raid is a good one, it gives the people a greater chance to do raids. But then?? Well you got 3 single-boss-raid, of which two are also entry-level, and only Malygos was a little harder, mostly because people had to ride drakes.
Wrath also introduced Achievements, but let's be honest. That's a poor substitute for having a new dungeon to explore. I know that Sarth3D is the hardest fight they ever made, but Naxxramas is already boring, and you'll probably do it twice a week (10 and 25 man - version). I pity the people who actually did the original 40-man raids in 2006. I think they were bored instantaneously.
On Ghostlands their are least 10 guilds now who have cleared the content, and 4-5 who also did Sarth3D. But there's no new Dungeon ingame to look forward to. If there was, Naxx would have been of the raiding-list already of several guilds. Even in 25-man, a lot of gear is already taken as side-grade, not an actually upgrade.
Somehow I have the feeling Blizzard took the easy way, and every crticial note is pushed into the 'now more people can play all the content'-basket. Well, 1.5 years ago, when I reached level 70, I looked into raids, and I saw a lot of content that I maybe would never see, but that didnt make me sad. I could set a goal to reach, get exalted with Lower City, so I could get another key-part, finally getting the 'Masters Key', maybe set foot in Karazhan some day.
There is no such thing now, nothing to look forward to. Yeah, there will be a new patch, and we have fun for 2-3 months in a REALLY new dungeon. I just fear that this also will be too easy, with Achievements thrown in to make it 'hard'..
I suppose the second expansion, is the expansion of the Alts. If you can walk through all the dungeons 2 months after release, there is not much more then you can do then level alts...
Now, maybe if they put two 25-man-multiple-boss-raids in the new patch, that would be different, but I ain't seeing that to happen.