Desolace started out great and then went rapidly downhill. Felwood, well it also started out great. It went uphill from there.
The two ends of the zone are unchanged: enter, kill insane furbolgs, and then wander off wondering what was the point of that reputation you kept gaining. They took the old Timbermaw quests and tweaked them a little, made them funner and funnier.
The zone then sent me on a gradual crawl north, during which I would kill demons, and then get sent somewhere else to kill more demons. It had a real demon-killing theme to it. I liked that. It made it seems like there was an actual mission to the zone, rather than just randomly being sent on pointless, tangential tasks. "Kill a rat! Now kill a warlock! Kill a warlock rat! Now go gather some rat feathers!"
This isn't due to a radical remaking of the zone. It originally dealt a lot with the legacy of demonic corruption. But it did it better, with small improvements such as not putting the only FP in the far north, or if you were Horde you had it easy and it was only halfway up the very long, narrow zone. I particularly enjoyed the quests where I was sent to kill a demon hunter, which took an expected turn, which as you probably guessed, was to not kill him, but instead listen to him explain how the druids were being idiots. He had a point. Illidan was also featured, typically arrogant, impulsive, power-hungry, and not all that much of a betrayer.
There were a variety of small, heart-warming quest chains. I got to help a new protector tree grow, worked with a sickeningly sugary dryad, got tricked by some mischievous furbolg youngungs, and in the most heart-warming quest of all, a worgen sent me to kill various goblins.
Along the way I ran Ful'Farrak a bunch of times, not because I like the place all that much, but because I'd gotten one of the swords, and if I got the other I'd have an epic. ZOMG EPIC! Eventually I got it, after convincing the hunter who rolled need on it that he had indeed rolled need on it.
I wasn't quite at level 54 for Silithus, so I helped a dwarf kill more forbolgs and then realized that seeing the new Blasted Lands would probably be more fun than another tour around Silithus. And off I went. It started off strangely, with a few quests to remind me that the Horde is being led by a warmongering jackass, then I killed some worgen ghosts whose ships had crashed. But finally I got to something good: Fighting demons.
At first I was slightly annoyed. It looked as if the quest chain for Rakh'likh (epic quest back in vanilla, perhaps too epic) was just another "let's slightly redo a quest that players did in vanilla, ignoring the fact that players have already dealt with this major threat." But it was a little fuzzy about exactly what was going on and what had happened before. However it made it clear that three of the bad guys I'd killed as part of the chain were still dead. Okay, that was a good start. Reading the wiki, he survived my attack back in vanilla, which given that demons tend to come back anyway, is plausible. The quest chain takes place in the aftermath, with the demon hunter having gone to to the job himself, and getting wrecked in the process. I won't spoil it, but let's just say it made me wonder about the means used to achieve the ends, and the ending was pretty interesting. I'm guessing in another decade when The Bulldozers Move Around the Zones expansion comes, we'll see another followup to it.
Perhaps the best part was that finishing this quest is was put me at level 60. So now I can go fight more demons.
There is other content in the zone, but I didn't feel like sticking around. As a tangent I'd helped the murlocs and that was fun.
I don't think the leveling curve is as screwed up now. I was thrown off it by many runs of Scholomance and Zul'Farrak, as well as multiple full clears of BRD. That last one is probably what threw me off, because I think I got a couple levels in the process. That place is huge...