Karazhan is kind of in the middle of heroics, progression-wise.
Certain heroics are much easier than Kara and certain heroics are much harder than Kara.
You should have no problem with a group in level 70 quest/instance blues and maybe crafted epics running Slave Pens, Underbog, Steamvaults, the Mechanar, Botanica, Black Morass, or maybe even Ramparts with the right group comp.
However, heroics like Shattered Halls, Shadow Labyrinth, the Arcatraz, Durnholde, and now Magister's Terrace require much better gear than the others. Groups in mostly epics are practically required for these heroics, not to mention needing almost perfect group comps to pull them off.
It is also of worth to note that Karazhan can basically be broken up into 2 sections. Everything up to Curator is fairly easy mode with the right group, whereas Curator is a gear check. However, if you can down Curator you probably have the gear to clear the rest of the instance. Most of the encounters after Curator are not nearly as gear dependant AND have some kind of gimmick that makes them easy.
Illhoof: 1-2 locks spamming SoC and a /target Demon macro make this fight almost trivial
Aran: 2-3 people who can spell interrupt make Aran a joke.
Netherspite: having people who know how to tank a beam make Netherspite easy
Chess: ZOMG Medivh cheated!!!
Prince: If you have the DPS to down Curator in 2-3 evos you have the DPS to down Prince, it's just about decent infernal placement
Nightbane: 2 priests to Fear Ward your tank make Nightane pretty easy.