This is going to be fun.
I spent the evening re-doing talents, re-learning skill, and fixing up action bars for Aetherna, Laenshield and Aeven - my trinity of dps, healer and tank. Then I went out and killed some random mobs in Dragonblight just to try and get a feel for the new abilities.
Confession time: I didn't do more than skim guides on the new talent trees, glyphs, gems, etc. I just waded in and picked whatever looked fun for talents, learned some new skills, and reforged a piece or two to get some mastery. Just enough to get up and running. I'll worry about making more optimal choices later, when it actually becomes apparent what those choices are. As I've been working on old world and BC-era reputations lately, being at the absolute peak of my game on any of my characters really isn't a primary worry.
Little or no change on Aeth - playing as an arcane mage is largely the same, modulo the mana conservation issues. Highlight of the evening was putting two points into the Nether Vortex talent. Automatically apply Slow when you hit a mob with an Arcane Blast? Yes, please! While Aeth has generally had two arcane specs - one for leveling/PvP, one for raiding - I'm thinking that now's a good time to branch out. Putting Icy Veins out of reach in the frost tree takes away the reason for the second raiding-specific spec, anyways. So she's going to go arcane/fire, and play around a bit with Blast Wave. Yum.
Laen and Aeven saw more major changes - lots of talent changes, lots of ability changes, and completely rearranged action bars as a result. Playing Laen as shadow seems relatively unchanged, but it looks like healing is going to be a slightly different game. On Aeven... oh, my.
On Aeven. Things are really different. Playing as protection feels much more reactive and less rotation-y. Playing as ret is going to require some getting used to - I must have been doing something wrong, because her damage output as ret was about 60% that of her damage output as prot. The Holy Power mechanic is going to take a little bit of getting used to, but overall, it looks like a win.
Reforging looks very interesting, and it adds another dimension to the gear game completely. Aside from talents, glyphs, gems, enchants... now you have another dimension to consider when you're trying to get your gear juuuuuust right. More importantly, it depends almost entirely on what other gear you have, because you can't get it exactly right - it's 40% of stat A into the same amount of stat B, apparently. So, for example, Aeth is currently sitting at something like 0.02% under the hit cap - but in return, she's got a bit of mastery on her gear now. Her next gear upgrade is going to require a re-evaluation of her reforging, though. Mmmm, I smell a reforging add-on coming in the wind...
UI changes, glyph changes, gem changes, guild tab changes, yadda, yadda, yadda. There's a metric ton of stuff to look at in this patch, and it will probably be a couple of weeks before it all settles down and I can get everything arranged to my satisfaction... just in time for Deathwing to rear his ugly head.
Bring it, Deathwing. Bring it.