I wish I had alpha acess, just to test personally the stuff they are implementing. For the few specs I'm following, the changes are mostly shit covered in shit and the reasoning behind those changes are retarded, to say it mildly.
Where to start? Let's go from arbitrarily removing skills because they don't like them or because [insert random reason here].
Let's say we start from Mistweavers: the whole mana, chi and mana tea mechanic is gone, statue is gone and made a talent, fistweaving is gone, the spec also loses Touch of Death and will be forever stuck in mana starvation mode according to Blizzard, because reasons (there is no spirit boost in later tiers to make up for this, unlike the previous expansions). Apparently healers won't have to be GCD locked or follow the ABC paradigm anymore (Always Be Casting) that made padding meters a sort of minigame by itself. I believe, if this shit goes through, you are going to wait hours in queue for healers, they are making a thankless job even harder to stomach, especially when you'll have to drink every other pull and those retarded superheroes tanks won't stop and complain that they died because "healers suck".
Let's move to hunters: they are making SV one of the most uninteresting melees of all times, pruning skills such as Disengage just to name one that could have added some mobility to the spec, they all got a serious hard on for this MM dark ranger "fantasy" where you summon skeletons (wtf does this have to do with hunters?), meanwhile BM is there sitting there with a thumb up its ass waiting for focus to regen based on RNG procs, since having builder-spender isn't appreciated anymore and Celestalon (poor guy taking the piss for the team) said something like "if you are GCD locked focus becomes meaningless, so suck it up and wait for buttons to light up before pushing them" (paraphrased of course), which is going to be paired with "just pop enrage" in the hall of fame of retarded things spouted by a developer.
Shadow priest is becoming a convoluted mess of a spec, but at least with all that haste, it'll be frenetic to play and give a new meaning to the "GCD locked" expression. I'm confident that they'll manage to nerf the fun out of it before release and making a shit-tier of a dps class, like it always was. Sucks I won't have Life Grip anymore (glyphed, to save my arse usually).
Discipline has become... I don't know, a fucking lot of work for nothing is what I suspect. Good riddance to PW: S spamming, but this short duration atonements, must be field tested before fully juding them. It won't be a relaxing spec for sure with so much target swapping (or macro galore), which I kinda like I think, as long as it's rewarding to master.
Holy priest: again Celestalon said it's not going to cast something every 1,5s and Renew will be changed to shitty level of healing so you'll enjoy the wonderful spell named "heal" much more, which means it'll be such compelling gameplay that I'd have to slap myself to stay awake. At least there is discipline.
I didn't follow much the other classes/specs, but if forums are an indication, all the ones I read are not happy at all (which is standard whining in front of change I guess), because the devs are making most specs brainless to play (see Beastmaster hunters), with few little things to look for or specs that are such a gigantic mess with no AoE capacity at all (for example subtlety rogues). Just using this example, I think rogues asked about some form of decent AoE for Subtlety, because in a world of artifact weapons to be levelled, swapping specs for ST/AoE will suck gargantuescan elephant cocks and when answering about the issue, if I understood that right, devs (poor Celestalon again I think) said "haha, we don't care, swap spec or something, we're okay with some specs doing blowjobs in certain situations" (paraphrased of course).
I read that Arcane mages are mildly satisfied, maybe some other specs are okay for those diehards that never play anything else, but I didn't delve too deep, I follow mainly the classes I play the most.
This been said I don't like their "new" idea of tanking and healing, I loved WoD tanking, it was the only well made part of the expansion and healing was okay-ish too, if only because tanks could help themselves for a few moments, while healers saved the rest of the group/raid. Aside from too much Uplift spam, healing as a Mistweaver and Discipline/Holy priest was quite fun. I enjoyed paladin less and druids with Germination had a fuckton of shit to keep track of, which made them interesting (together with spamming Wrath proccing heals for low healing periods). Shamans were damn good healers as usual, but a tad more boring without castable on the run Lightning Bolt to regen mana like in the past.
It's alpha, so I expect a lot of changes, but if history is an indication, many of those will suck. I hope for the best.