Loss of low level content - I WANT to want to level a new alt, I just have no motivation to whatsoever, with the abysmal, abysmal changes of Cataclysm, turning every single fucking zone into a railroaded - take 2 quests! return! take 2 quests! return! take 2 quests! return! Literally makes me nauseous. Oh and every dungeon is tankable by a priest, or a warlock, or a mage. Nice. Really allows you to get up to speed with group work, your classes' abilities etc.
Loss of sense of community - Every server I played on in Vanilla/TBC was literally alive with community/chatting etc. Groups getting together for SS/TM PvP, massive raids, server rep, top tier PvPers helping each other in the HWL/GM grind. People hanging around in their cliques in Shattrath, while getting to know who was a great tank/healer/dps for daily heroic quests etc. Nowadays.. who the fuck cares. There's no need for any of that. Click a button, free raid, afk. Click a button, free BG, afk. Click a button, free dungeon, impossible to wipe. Spare me.
Not enough to do - disagreed. There's more than enough to do. You're only bored if you're boring, as some random band once said.
Easy everything - to a point. Sadly, everything to do besides high-level Arena/RBGs and top-level Heroic Raiding is absurdly easy. CMs are the only slight exception, and that's only when you're learning the pulls. There's literally nothing challenging anywhere else - and there needs to be. There needs to something interesting between raids/arenas. 5mans in MoP are an absolute aberration. Absurdly few, absurdly easy, filled with boring, stupid, immersion-breaking RP. Even WotLK, which had the easiest 5-mans besides MoP, at least had a huge variety.
Random PuGs - absolutely crippling, for quite a few reasons. Firstly, as above, loss of server community. You no longer make friends, teams with people on your server who're great in dungeons, or just fun to be around. There's no reason to do so. You just click a button every day, et voila, there you go. Secondly, since it's so faceless, with people you'll almost certainly never see again, there's no reason to play well, there's no reason to not AFK, there's no reason to be courteous, or polite. You can just swear, abuse, spit, kick, insult, afk, attack the wrong targets etc. Not only will you rarely so much as cause a wipe, but there are literally no consequences. You can't be "blacklisted" from future LFRs if you're a douche, or AFK the whole thing etc. Thirdly, since it's the status quo in grouping at the moment, fights have to be tuned around the lowest common denominator, which is LOW, VERY LOW in random PuGs. This makes the group content even MORE trivial/forgettable for those who actually care, y'know, the ones the game should be designed around.
Loss of sense of accomplishment - another big one. I remember progressing in early WoW. Sure, there were massive negatives, but there were amazing positives too. I remember the first time we killed bosses like Nef, or Twin Emps, or C'thun, after weeks/months of challenging attempts. It felt fucking AWESOME. The first time we killed Twin Emps, and were able to clear to C'thun, and discover a major badass waiting around the corner. It's just unforgettable. There's NOTHING like that now. Too many difficulties. Unless you refuse to do anything but Heroic, or Normal if you'll never touch Heroic, you're just spoiling the fights/sense of progression/sense of excitement for you and your guild by seeing everything on LFR. And you HAVE to do LFR if you want the most out of your character, especially at the start of an expansion. Killing Garrosh on LFR, then Flex, then Normal.. yeah. There's nowhere NEAR as much excitement when you kill him on heroic when you've already killed him numerous times on other difficulties. Still some, just not as much.
Weird or bad lore/setting - pretty much completely personal taste. I think MoPs setting was fucking awful. Could they have been any less subtle about the Asian influence of the Pandarians? Seriously? I don't really care other than that, it's their story, tell it how they will. Just don't force too much RP down my throat.
The last 2 points kinda just tie into the above ones.
I'll add though - still greatly looking forward to WoD, but yeah, I'm not exactly holding my breath for revolution.