What we didn't really expect is how much different the place would feel 10 levels later, both of us geared in Ulduar/ToTC 10/25 gear, and playing possibly the strongest tank and healer combination possible. To say we destroyed the place would not be inaccurate: only Hex Lord Malacrass was a significant challenge due to his ability to use Soul Siphon to acquire healing abilities that a DK/Druid combo just couldn't purge off of him. (Trust me, Hex Lord with Mark of Blood? Extremely nasty. Follow that up with him spamming Rejuvenation on himself and he can get to full health from almost dead. It took us 10 minutes to kill him.)
Still, despite the fights not being nearly as hard, they weren't pushovers either: several times on Nalorakk I came very close to death, and Halazzi still hits very hard with his Sabre Lash, which we couldn't really split (taking 12k as a 33k tank isn't nearly as bad as when you're lucky to have 20k, however). It was illuminating to see all the fights again from the perspective of a class that would never have been able to do them. The fact that Malacrass has a Soul Siphon ability for DK's never even occurred to me.
Since we know that Azeroth is due for some big changes, it's kind of my mission to run as much of this older content as possible before it might well vanish entirely. I want to get my DK all of the achievements that my Shaman and Warrior already have, run all the old world and BC instances and raids, maybe even get Loremaster before it's gone. Even more important than that, to me, is to get to see how much stuff I can do stripped down. How few players can we bring to Hyjal and still clear it in a reasonable time? Can we do it with two, or will we need four? (We're going to try with four first and if that goes well, maybe pare down to two for the next attempt.) I've already solo'd MC and Onyxia, can I do BWL? My guess is no. Razorgore and Vael will probably trip me up. But I'm willing to try. But for other things, like Sunwell, I went back primarily just to get to see the old fights again, and the fact that we had 10 players didn't really even enter into it.
To be honest, Sunwell was still reasonably hard even with 10 level 80 raiders in full Ulduar/ToTC gear. We weren't there to see how few you could bring, we were more there just for players who'd started late in BC or in Wrath to get a chance to see what they'd missed. Frankly, I'm really glad I went along, as the fights are still crazy epic to watch unfold even if you're significantly over the gear curve, and frankly we wiped more than once: this content's not a joke and some of it is still some of the best designed encounters yet in the game.
Also, and I'll admit it, part of the reason I go to see the old content is to try and collect the loot that defied me. Yes, that's right, I finally have a Spinal Reaper in my DK's bank. Wouldn't drop in seemingly thousands of runs on my warrior, but I finally got it. And I will be darned to heck if I don't keep running BWL until he gets an Ashkandi.
So, basically what I'm asking is two fold: what have you missed, and what do you miss in older content? What did you never get to see, or are suddenly realizing you might never get to see again? Are you putting together a group of level 60's to raid classic content with the XP turned off, or doing a fun run stampede running through Black Temple to zerg Illidan down? Are you looking to see what you never saw, relive old raids of your past, or collect some cool loot you missed one way or another?