Yesterday husband (tank) and I did Karazhan, it wasn't as straightforward as just entering the instance though, we had to complete a quest chain in order to get the key and although this took us one evening, it was interesting because when levelling my Priestess we skipped many of the Burning Crusade dungeons and so to see them and get the achievement for them made for an interesting couple of nights.
I especially enjoyed the Opera Event, and as you can gather from the blog post title, we encountered Romulo and Julianne, and also the Chess Event, I thought we may have a problem as there was only two of us, but husband took control of the King and I took the Warlock and we just aimed at the Human King and dealt as much damage to him as possible, ignoring everything else. It worked as a tactic, and we were soon moving on.
I felt Karazhan lived up to what people have said about it, but since we were completing it at level 85, it was very easy, and we didn't have to pay any attention to tactics. We were killing trash faster than my spell cooldown but even so, I'm glad we did it.
I think that in it's day it would have been an amazing and somewhat tough raid, I dont think I got to see the best of it being such a high level, but its definitely worth seeing.