Ok, @charmtrap this is for you.
Nazjatar is a hot mess. It’s clearly designed for flight, so until you unlock flight travelling is a nightmare of trying to get from point A to point B. Phasing is terrible, the worst ever seen in WoW. Not only do you experience the clicky disappearing as you approach it, you also get the “Surprise! You’re now surrounded by Naga” phasing. The mob density is insane in many areas. You will die.
Some of the daily quests are terrible and you will not do them.
Mechagon is much better than Nazjatar and feels like it was developed by a different team. It does not have world quests, however, so leveling up Rustbolt Rebellion faction is slower.
If someone calls out a rare spawn on either island, you better be super close or you will not get it, at least without flight. Bonus - both islands have daily quests that require killing three rares.
The Azerite system is improved… but it’s still a giant shit-sandwich compared the delicious but messy burger that was Legion’s artifact and Legendary systems. You still need to grind AP. That’s fun, right…?
Completing all quests and WQs on each island will run you 3-4 hours each day, depending how shitty some of those quests are. That’s significant.
All the classes still suck and are unrewarding to play. There is one ideal talent configuration and any deviation is a DPS / HPS loss. As a frost mage main I am sooo sick and tired of running Bone Chilling and Glacial Spike, but every other talent combination is a DPS loss. I loved Lonely Winter + Thermal Void in Legion.