On the plus side, I think it may be impossible for me to run out of mana when soloing. VT/Replenishment is a slap-in-the-face joke when it comes to mana return, but the new mechanics of Spirit Tap had me ticking back to full mana between pulls. This won't help much in an instance since I seldom get the killing blow, but it will make levelling a breeze.
On the down side, in my limited experimentation, my DPS looks to be lower after the patch - and this is after I swapped out to better gear. My critical strikes are much larger (3700ish instead of 2400ish), but they coupled that with overall nerfs to most of our other damage spells. I am going to wait until I can run a set of daily quests to see what my numbers look like at the end, but for now it looks like Blizzard may have put one over on the priests. It's possible that my damage meter is borked, but it appears that they have compensated us for removing all of our utility (they are already promising a nerf to VE) by reducing our damage output as well.
Oh, and with the exception of my azure dragon whelp, all of my pets and mounts are gone. Blizzard's initial response was a somewhat cocky, "Don't sweat it - it's just a display issue. We'll have it fixed shortly." to something more akin to, "Um, we're hoping that we can somehow restore those for you..." I know that vanity pets are not a game-breaker, but I jumped through a lot of hoops to get some of those pets, and I am going to be sorely miffed if I don't get them all back.
I am also unimpressed that the game has not credited me with achievements for clearing old-world content. The only one that it has credited me with is Onyxia's Lair, and in fairness to the game, I'd have a good argument if it didn't credit me with that since I still have the Tier2 helm sitting in my bank. I am not going to go back and clear MC, and BWL, and AQ20 and the like just to get my deserved credit for those. I may strive for a couple more titles (I've gained 3 since the expansion: Jenkins, Diplomat and Guardian of Cenarius), but I don't think I'm going to sweat over the buggy achievements.