For what it's worth, most of the quests work fine. There's a _few_ that have issues, but the vast majority work just like they did in 2010.

The largest issue I can think of that actually impacts overall gameplay is the thread system [0]. It definitely works, but currently threat at times isn't given or reduced in the correct amounts. The most common way this manifests is Growl from Hunter pets not properly taking aggression away

[0] - https://github.com/azerothcore/azerothcore-wotlk/issues/5985