I find this tier a clear 50/50 split really.
Half of it is fun, intuitive design, the other half is tedious and tiresome mechanics with poor design ethos and implementation, along with some archaic reversions to the old 'just add interrupts or adds' to make it harder. I love that my class got love which is swaying me toward enjoying it more, but heroic content wise (Normal modes I enjoyed when we were doing them, without a doubt) has a real hit and miss air to it, with some fights really translating well difficulty wise and others translating to awkward to handle and RNG-themed problems.
However, it beats out a majority of WotLK content, and I wasn't expecting the expansion to hark back to TBC's perfectly tuned way, so all in all I'm pretty happy with it, after all with all the radical things Blizzard were saying pre-beta, it could have turned out far worse