Apparently 2.07 made him invulnerable to almost any type of interruption, and players aren't happy about it. I'll still say the fight's not completely impossible (there's a strategy where you can all group around him to keep him from blinking, and then hide behind a pillar to avoid line of sight on the AoE, and another strat where you just do what you can to time heals with the AoE and keep clothies out of range, and I'm sure interested parties will include more in the comments below), but I haven't done it myself since the patch-- I've just heard it's very, very hard.
Additionally, Illhoof, a boss in Karazhan, got a nice undocumented buff-- his shadowbolts hit harder, as does his Imp. Players at that level (that's a fight I haven't done at all yet) say he's so hard he's not even worth the drops at this point. And another boss in Karazhan, the Maiden of Virtue, got a little bit of a buff on her "Repentance" spell, but apparently the fight's still easy.
As of this writing, there's no official Blizzard response to any of this, which could be taken either way, but is probably a pretty good indication these are all working as intended. Sethekk Halls, it seems, just got a bit harder.
Update: Our own Eliah Hecht reports that Tseric has said "working as intended" on the Illhoof and Maiden buffs, but "communication breakdown" prevented it from showing up in the patch notes. More info in the comments.