For what I've read so far, I don't have my hopes up for Legion. I'm sure I'll find an enjoyable class if the monk will suck gigantic cocks by release time, but holy shit, it's like they are trying hard to remove fun and introduce blandness. Mistweaver becoming a boring healer just like everyone else, Brewmaster losing another ton of shit from the spellbook, including fucking Touch of Death for what I read, which will be WW only (a shit, boring, fucking useless spec that maybe 4 people play world wide) and that will also trigger 8 seconds after application.
According to their most recent blog entry, once again they are taking away stuff from tanks, so that they have to rely more on healers (like healers don't get enough shit already) and making so that if tanks don't use active mitigation (or what will be left of it), the difference won't be so pronounced, like this would help the other players find competent tanks.
My second beloved class, the priest, is being twisted in random directions: I get the theme of shadow being, well... shadow, holy being light, discipline being halfway, but disc is changing its playingstyle and so far it seems it's a lot of work for little returns: after coping with Renewing Mist going on random players so I could use Uplift and pad the meters, I can't say I find buffing someone before I can heal him an enticing and exciting mechanic, quite the opposite, it's pretty much a crock of dry shit. It will also require a large amount of macros to work decently
Shadow as usual will have to use 25 globals to do a fraction the AE damage warriors and rogues do with one keypress and still lag behind in single target (which on par with shadow history, except maybe during Cataclysm), plus this uncontrollable voidform is a stupid idea and should be tossed in the toilet before it's too late.
Holy looks quite good, I give them that, considering it's going to get Complete Healing (well, yeah, almost) and for the rest remain a standard healer.
I'd also follow druid and hunter changes, but I fear what I may read. Before WoD I disliked class changes and ability pruning, release confirmed my opinions, now I'm thinking that, even considering the current as alpha state, they are not going in a direction I like, except (in some cases) thematically.
On another point, I want to understand how the artifact catch up mechanism is going to work, because I can't imagine myself levelling as a healer, but having to do a week of artifact catching up before being dungeon or raid ready would piss me off.
I love this game, but some things *are* getting worse over time, class design for once. Just to mention one, I remember fucking around at the end of MoP with my arms warrior, it was quite fun, then WoD came and I was watching Rend tick... so beautiful!