I, like many other players, spent the better part of the morning running the new 5man Magisters' Terrace instance (and yes -- it is "Magisters'," so there is actually more than one Magister in it), and while not everyone is thrilled with it (I know some are saying that it's too hard), I love it. I pretty much agree with AA -- it's not that hard when you actually figure out what to do with CC, and get a handle on the fact that even on normal difficulty, this is a dungeon that doesn't let up.
But my favorite part of the dungeon is just the fact that Blizzard put their money where their mouth is on this one -- for a while, they've been saying that they wanted a five man to be like Deadmines, in that it felt like the end of a long storyline. And MT (which is what I think it will eventually be called by most players, since who really runs Mana Tombs anymore?) is definitely that -- I won't ruin the lore too much, but it works perfectly as both a cap on what happened in Outland, and as a sweet preview to Sunwell Plateau. I never thought we'd meet some of those names in a five man instance, but I loved it, and we'll see more of that in Wrath for sure.
Plus, the encounters are fun. Unfortunately, there's nothing super new -- Blizzard cribbed directly from Warlord Kalithresh for the first boss and Curator for the second (boy, AoEing the little guys before that is exciting, isn't it?), but the miniboss battle near the end really does play like a little PvP-ish PvE (similar to the .5 upgrade event in BRD). All in all, I think it's a great instance, and a fun way to cap off five mans at level 70.