(Everything here of course is just MY own opinion.)
I apologize for the wall of text in advance.
I began playing WoW in WotLK (and proudly accept the title of being a "wrathbaby") and although I am not having as much fun in MoP as I was then, I blame that on the fact that when I was playing back then I was 19, not working a serious job, and had ... far too many free hours to blow on the game with friends of a similar age.
Now that I'm 22 with a 50+ hour a week job, I can't put as much time into the game. However, I remember spending a SIGNIFICANT amount of my time in WotLK AFK or just riding around in boredom in Dalaran. Cataclysm had this same trend.
In MoP I've never once felt like I had nothing to do - if anything I've felt there is just too much to do :P ...
BUT - isn't that the sort of feeling we wanted in WoW? To have so many options that we weren't pigeonholed into doing 1 or 2 things?
MoP has been a total breath of fresh air in that regard. While I am not crazy about the new scenery or lore, I respect it for what it is. I think with the game in the state is in now, whenever their next expansion comes out (which I'm assuming will tie back to more popular lore such as The Legion or Emerald Dream) people will be very engaged.
There are only 3 things I have hopes for Blizzard will change their stance on for MoP and future expansions.
1) Talent System - while watching Blizzcon in 2011, I was all for talents that really MEANT something. However, in execution of it, for some reason I just can't get into the idea of leveling up, and then a void of nothing. Just "grats, you leveled." I miss the "illusion" of choice - yeah, that 1% crit per talent level might not have you doing triple the damage, but you still felt you were improving your character. I never had a problem with cookie cutter specs and from the players I've talked to, they didn't really either. This one focuses more on the leveling aspect of the game... but IMO this talent system just isn't great.
2) Valor Items gated behind Dailies (and the garbage that was ilvl 450 JP Gear.) - This actually had me unsub from WoW as soon as my Annual Pass ran out - it's not that I don't like dailies but in no way do I feel your ability to get gear should be the carrot on the stick for them. From what I understood, "badge gear" was introduced as a method to reward players for their work if they weren't lucky with drops. It was a way to gear up. If you didn't get that plate helm in your 10 heroic runs, here! Buy one for 2200 JP! Or whatever that worked out to be. You got your valor to buy that epic piece every 2-3 weeks. You felt good about buying that helm because it was maybe just a little worse than the one that comes out of a dungeon, but it wasn't handicapping you.
With ilvl 450JP gear, it was a turnoff for me personally knowing that the gear was next to worthless in the sense it would need to be replaced by heroic gear. It wasn't close to as good as a 463 (especially when you factor in things like sockets...) It was smarter to convert JP to honor and buy the higher ilvl honor gear. I never understood this call.
And while I understood Blizzards mentality of "If you raid, you'll get gear anywway so you don't HAVE to do dailies...." - for competitive players that wasn't the case. For casuals I just feel it took away a gear option for them. Yes, casuals don't NEED raid gear if they aren't raiding, but isn't the whole point of the game to get better gear to kill tougher things? (or maybe you know, just to look cool?) ... If you dungeon capped valor, unless you did dailies you couldn't spend it. Awful, awful design IMO.
3) Bring back Reputation via Tabards - For all of Blizzard's talk of we want YOU to be able to control what you do in the game - they sure pigeonholed PVE players into Dailies. I'm not saying Tabards need to give massive amounts of rep to the point you can get exalted with 2-3 factions in a week, but don't CAP our ability to earn reputation via dungeons to the point where you'd be dumb not to do dailies!
Without the commendation, a day of dailies with Shado-Pan gets you roughly 1500 rep. A daily dungeon gives you 300. I'm not saying dailies shouldn't give MORE (I think it's a smart idea actually to get players who want to be in the world, out into the world) but the level needs to be brought up to that. If somebody would rather spend 2-3 hours spamming dungeons to get 1500 rep, rather than do 30 minutes of dailies, what is the problem there? One method is clearly faster while not alienating the people who simply don't want to do that method.
Some people just don't like dailies. Some people just don't like QUESTING period - I don't see blizzard putting caps on how much exp you can earn via dungeons though. Why isn't rep treated the same?
Literally keep everything else the same (expansion long immersive legendary quest-line, 12-13 boss tiers, the questing style, pet battles ect.) and while I don't think this game will ever hit 12 mill subs again, we'd have ourselves a very very good, main/alt friendly expansion.