Just the fact that you aren't running the length of the zone over and over is a big improvement for me. Between that and better quest clustering, it's easy to see why the levels are flying past.
I ran around through all the cities. Some haven't changed much, but they all seem pretty good. Malfurion Stormrage is in Darnassus if you haven't spotted him yet.
I've run a shaman through Dun Morogh and, comparing it to the time I levelled a dwarf warrior through shortly before joining the original HoJ, it did seem a lot better.
I've also been questing an undead warlock on the Turalyon server through Western Plaguelands. Very interesting changes, completely revamped after the work the vanilla factions have done reviving it. There's also the Battle of Andorhal, which I believe I haven't seen the end of yet, with a number of familiar faces making appearances, and some surprising and extremely cool questing on behalf of the Forsaken.
I've just reached the Argent camp next to one of the middle farms. It's Argent Crusade, the Wrath faction. Get yer rep if you didn't manage to max it out with a champion's tabard.
I had just arrived at the Argent camp and was picking up quests, and as I ran towards the Forsaken standing there my screen went red. Now, I've had several weeks of technical difficulties with my laptop, so I made an effort to remain calm, walked around a bit to see if maybe it was just an area of red cloud, then started to log off.
Then the world exploded in flame, instantly killing me, and I got
Stood in the Fire.