I would recommend just chilling and saving the urge to play for legion. The prepatch is only a month or two away and it will bring tons of players back.
...and I fear that after the novelty wears off, these people won't bother playing the xpack or if they do, it'll be a one month trip to watch the content. In terms of gameplay, I've never witnessed before such an abysmal reception of the class changes, considering that a lot of the alpha was done by focus groups of 13/13 M players (but not only), there are very few specs that are quite happy with their changes, if "happy" is not too strong of a word.
I can recap the feedback in a TL;DR format, this is what I gathered from multiple sources of alpha/beta players and theorycrafters. I did not follow the 35 different specs, which are pretty much classes on their own nowadays, but it gives you an idea of where the current feelings are.
- Death Knight: Blood seems playable finally, frost is shit and unholy is meh.
- Druid: resto is good and fundamentally the same as before except a new mastery, balance is better than WoD (worse was probably impossible), feral is boring and still has Savage Roar, aka a retarded buff to keep up that fucks up the whole priority list, Guardian is good, more fun than before and has a fuckton of hitpoints, which is always lovely to see.
- Hunters: you can probably salvage Marksman, maybe and that's a stretch. Beastmastery and Survival should be taken out and put out of their misery. I don't think any serious hunter will every play one of those in their current sorry state: they suck mechanically and they are boring as dry shit. The pruning on this class is also atrocious: depending on spec you may lose Camouflage, traps (all of them) shots of some kind, etc. I would personally pack the shit of this developers team, push it out the door and fire them in a parking lot, because it's frankly ridicolous what they did.
- Mage: Arcane people seemed happy, Frost had a few tweaks to be done and Fire people were quite unhappy, but it seemed there was hope even there.
- Monk: Brewmaster not happy, Mistweavers are split, it's certainly much more boring and lost all its uniqueness, but it may be powerful enough to be considered interesting, except MW has no real utilities. Windwalkers I have no idea, sorry.
- Paladin: pass. No clue.
- Priest: well here things get interesting. Shadow is pretty much a well received revamp, still lacks in the burst AoE department, but the class seem cool, both thematically and for the gameplay, which considering the insane (haha!) amount of haste it can reach, it'll be the most action packed frantic smashing of buttons ever seen in WoW. Surrender to Madness has the potential to be the most fucking broken personal cooldown in the game, reports speak of over 1 million dps on 2 or 3 targets for more than one minute before the tragic ending (horrible death) and this with shit gear. Discipline has changed a lot, it looks fun on paper and effective enough for those who like the concept of an offensive healer, like the Rift Chloromancer. I don't know how hard it's going to be managing atonements, but it can't be terrible. Holy is also gaining a lot of neat tools and really large heals. The class as a whole seems in a great position to enter Legion (and I'll main it again, fuck playing a broken class, I want a fun one).
- Rogue, shaman, warlock: honestly I didn't keep up with the changes, my info are outdated, so I'm not going to comment.
- Warriors: dps warriors say that Arms is better than WoD (anything is better than WoD Arms, *even* watching paint dry) , but still quite boring, fury is slightly better, but not enticing enough, protection ranges from "meh" to "okay-ish" depending on whom you're going to ask.
The general feeling is quite negative, first because nobody likes to lose a shitton of skills they used for years, some for more than a decade (e.g. Aspect of the Cheetah), secondarily because the changes to skills and talents remove the interaction among them, as way too often there is a determined set of skills that is better than everything else and again that set of skills/talents is mindnumbing boring.
I followed all changes from expansion to expansion, but I've never heard so much negativity. Maybe it's because a lot of players today are just whiny cunts, but the difference from gaining new skills (TBC- WOTLK) and losing them to pruning or lol-class-fantasy (MoP-WoD-Legion) is huge.
Underrepresented specs, such as Ferals for example, have been largely neglected, with shitty artifact talents, lazy developing of the class and little to no mechanical changes since... forever, fucking Savage Roar again is there to put this under the spotlights, jeez...
One comment I read made me giggle, the question was "what will you miss in Legion?" and one answer was "People, because Legion will not keep them". It sounds awfully true.
I'll play a priest, I should say a shadow priest, the changes are interesting and the gameplay is improved from the current state, even considering the loss of Devouring Plague and Psychic Horror. I get to keep my PW:shield and gain Shadow Mend to heal myself and others, I gain amazing levels of haste and while there are a couple of things I don't really like a lot, I think I can learn to live with those, as long as the legendaries class specifics are not overly rare to get. I think the difference between a capable shadow priest and a crappy one, won't ever be so large tho, which is good and scaring at the same time: first because there is always someone better than me and I don't like to be less good than someone (!) and second because I fear for future semplifications.
My suggestion is to find a class you're interested in right now, gameplay is pretty much set for the time being and focus on that as a main. I don't like leaving the monk behind, but I really dislike ALL the changes. Tanking mythic dungeons this week made me think of all the skills I won't be able to use anymore, such as Dizzying Haze, Touch of Death, etc. and I was smashed. Back to priest, good old priest.