Levelling was linear and stale. Though some of the zones were aesthetically nice.
Hard dungeons were fine for me, but pissed off the casual crowd.
T11 was fun for me, semi hardcore raiding. Horrible for casual crowd.
T12 was garbage except Ragnaros.
T13 was literally the single worst content patch in the history of MMOs and the most horrible end to an expansion ever that lasted for around a year....