This question was brought up by a post from Lavata of the Sentinels US realm. She asks why Blizzard made the Magister's Terrace so damned hard. With mobs that "are worse than trash in Kara" and Bosses that are easier than some of the trash pulls, Lavata says that it is far too difficult for your average 70. "MaT fails to fill the spot it is meant to in progression" to paraphrase.
I think that Lavata, and many others who eagerly fly their way to the Isle of Quel'Danas in anticipation of a run through MaT(for lack of a better abbreviation), are making on mistake in assumption. They assume that this will be just another 5 person just like the rest we got with TBC. It isn't. Why would it be? It is a dungeon we get as we all near the next phase of the game, Wrath of the Lich King.
Look at this like... the baby Naxx of the TBC era. It's not the big raid instance, as Sunwell Plateau fits in there. It's the baby one for the non raiders or those just looking to get more gear from rep rewards. It will be hard. Harder than any of the other 5 person dungeons we have so far, and that is fine because it should be hard.
Another thing to consider is something that Drysc points out in the thread. When TBC came out, people were even at the high ends of the dungeons still banging their heads on the wall of the low TBC dungeons like Blood Furnace and Slave Pens. Hell, some people still haven't done those dungeons because of their earlier troubles. Only one of my 3 70s has ever fought his way through the Slave Pens dungeon.
This is the early head banging phase of Magister's Terrace. It's the point were we try out the strategies, attack fights from different angles, and see what works. We also see what doesn't work and how we can fit in those classes who are the outsiders of the dungeon sets, the Ret Paladins, the rogues, the hunters and more. Give it some time, Lavata, It'll come.
Of course, as always, your mileage(and gear) may vary.

This is a great article. I just have to share my favorite abbreviation for Magister's Terrace: MrT.
Eh... I don't think it's really any harder than Shattered Halls or Shadow Lab. Of course, that could be because I've run it with middle-to-well geared people (first time all in Kara gear, second time a mix of 70 blues and PVP/Kara gear) but I think if you've been 70 for any length of time you should have the gear to pull it off.
I ran it once on my warlock and once on my warrior. It stinks to tank without much CC, but it's do-able. The boss fights aren't too hard (First two are based on other fights, last two a little newer - Third boss is like the 5v5 match from hell).
I kinda liken it to Shattered Halls, with a bit more strategy on the boss fights. People are just whining at the moment because it's new, and peoploe haven't worked out how to skip half of the instance and instantly one-shot the bosses yet.
And some of the gear drops in there are NUTS for how easy it is.
Aly, that is pretty much the point I made, it's hard because it's new, just like Ramp, BF, Underbog, SP and the other dungeons in Outlands were when we all started out.