I'd say it started off strong, but there's alot of issues currently that they won't address or change:
-Titanforging mechanic: There's really no excuse to be able to have a piece proc titanforge and be just as good as a mythic boss piece. It severely undervalue's the accomplishment to me personally and I'm sure I'm not the only one.
-Legendaries: I really can't fathom how they continue to make you grind to upgrade each individual one every raid patch. Secondly, the RNG aspect is not "cool" as they claim and it's beyond frustrating especially when having a certain one makes the mage tower significantly easier (Sacrolash for Affliction Warlock for example). Or Guardian Druid's thrash bracers and many more. Call me bad or a scrub, that isn't going to change my point of view as I'm also not the only one who feels this way.
-Severely alt unfriendly no matter how much they claim it is: While I'm not the biggest alcoholic and does not concern me much, I completely agree with those that believe this to be true. Between World Quests and back to the legendary argument, I believe they could do a better job.
-Very bland boss fights: This is completely subjective, I get that. However I don't believe any of the raids this expansion even remotely touch how incredible I found WoD's raids to be. Every boss felt different, the mythic mechanics were very fun and engaging, and I just don't feel the same this time around.
I'd say these are the biggest issues to me personally.
Of course, just an opinion.