I have played WOW off and on since just after release (coworker was in beta and kept asking me to try it, once it was released I joined and was hooked) but MOP has been the first patch I didn't resub for. Personally the best times for me were TBC (Karazhan with friends, occasionally getting in higher tier raids as a sub) vanilla (so many great memories) and wotlk up to ulduar more or less.
In a game that has millions of players there are millions of stories and millions of reasons of why players play or quit, these are why I am personally not subscribed (even if I wish I could be, if TBC was going on I'd be resubbing tomorrow)
- no sense of community: LFR, LFD and CRZ have completely killed any sense of community: since there is no downside for being abusive most people seem to be, in the old days if you ninjaed something in a dungeon run the other player(s) would message your guild leader and you got a talking to, if you did it more than once you got kicked out, or your guild could even end up being blacklisted so you would never PUG again. You met people while levelling and ran dungeons together, and form friendships which sometimes led to guilds, and sometimes to various PUG runs, and in general again to a sense of community.
- difficulty levels are out of whack: in the old days there were easy instances, and hard instances, you brought your not-as-competent friends to the easy instances and carried them a bit, and it was fine, and it was fun. Nowadays it's super easy heroics, brainless LFR, and hard raids where most fights have a 'one person not as good can kill everybody else's evening'. In the old days it was possible to carry people in raids too, just look at how many people died on average on the safety dance in 'bad guilds' or mixed the polarity, but still it was possible to down the boss if at least 2/3rds of the raid was competent. Yes, this meant that the 'super hardcore' had a bit of a snoozefest at times, but it also meant that a LARGE part of the subscribers could do the content as it was written.
Now it seems that 'see the content' means 'tune it so drooling on random keyboard keys makes the boss go down' while normal and heroic are tuned hard in terms of mechanics. That might be good for the hardcore, but not for the average player (I shy from the 'casual' label because just because somebody is not as good at the game as somebody else it doesn't make them not care, which 'casual' seems to imply).
- game seems focused towards more and more time invested: in the old days the minimum amount of time you needed to play on a daily basis to do content was not nearly as high as it is now. People with less available time were still able to contribute very well, if they had more time they either had more alts or they did some of the OPTIONAL grinds (black thorium, furbolgs, ...).
Nowadays if you can't put at least a few hours PER CHARACTER a day you're going to get left behind, because of the dailies, reps and so on. It seems that Blizzard listened to the loud cries of people with no life but the game that 'there isn't anything else to do' and so added more 'things to do' but also made them pretty much mandatory.
- design constraints shaped by non-game factors: many times reading GC's twitter replies you get some form of 'well, we could do xyz and give you this, or we could do this other thing and give you a lot more, we can't afford to do both' usually in the form of 'you either get a new raid or a new dungeon, and we think a new raid is a better investment of our money' or 'you either get 3 new scenarios or a new dungeon, and we think the scenarios are better'. It seems that vanilla/tbc were games where the design was the priority, not how much it cost to implement.
Complex problems have complex solutions, but if it was up to me for the next patch I would:
- keep LFR/LFD but make them REALM RESTRICTED, you get grouped ONLY with people on your realm
- remove CRZ entirely
- free transfers for everybody once every 3 months.
- rework heroic dungeon difficulties, have a progression where you have easy heroics, harder and hardest, where hardest is HARD (say, quel'danas when it first opened where the 'pvp boss' was really rough)
- remove dailies as a source of gear, dailies should be for cosmetic/profession/gold purposes only, NOT gear progression
- completely separate PVP/PVE in terms of skills, remove gearing from PVP entirely, just have cosmetic 'skins' but stats remain the same
- remove 'guild perks/reputation' or make them baseline
- put back group quests, long keying quests, attunements, but make them all soloable
- add 'tank' and 'healer' generic NPCs to dungeons so DPS can still get runs done if they really want to, but don't make them too good (make them only walk, say, and pull every group) so there is still a push towards having a 'real' dps/healer
basically I would try to go back to what made WOW a great game for me for the first few years
- a sense of community in the realm, the chance to make friends and get to know people
- a sense of progression, where dungeons and heroics are real stepping stones to raids, and even if you can't raid you can still get a lot of enjoyment off them
- a sense of the game wanting you to play so you can have more fun, vs the game being a job
anyways, this is long enough and it's not like Blizzard would listen to me anyways, but I thought I'd put it out there.