Cataclysm had a lot of recycled content. If you look at Blackwing Descent, it is essentially Blackrock Depths/Blackrock Spire/Blackwing Lair all over again, in terms of art and enemies (they even re-re-revive Onyxia). Firelands felt a little more fresh, but Ragnaros is not anything new. Dragon Soul re-used Dragonblight and Wyrmrest assets, and every boss had this "ho hum, done this before" feel to them -- this was all made worse by the fact that the raid lasted so long (real time).