Ehm... I think all we can say was that Nax 2.0 was too easy (and lasted too long because Ulduar took quite a while) and that ToC was a failed concept. I see people bitching on these 2 things SO much and declare WotLK raiding a fail... I really don't see how :\
An other thing people bitch about is the hardmode mechanic. I personally like it as it does what it is supposed to do: Give "casuals" a chance to see all the bosses and give "hardcore raiders" the challenging fights and rewards accordingly.
Personally I would've liked to see a bit smaller jump from one patch of content (hardmode) to the next patch (normal mode). For example, if ToGC gave 258 gear, then maybe ICC normal should drop 261 gear or something. This doesn't make every item a raider has obtained obsolete at the start of the patch and some items can even be better than a 261 version because of how it can be gemmed or through socket bonuses. (Right now the only thing from ToGC still worth using are the trinkets).
This gives the casuals the tools they need to do the normal modes, and rewards the hardcore raiders for doing the last tier of progression, so they progress through the normal modes faster, so they can get hacking at those hard modes again!