As for the classes themselves, they almost all play like slower and slightly less interesting versions of their Legion counterparts. This is thanks in large part to the loss of one ability from each class that came along with Legion’s own AP dumping system: the artifact weapon, which added a unique ability to every spec in the game. The loss of these abilities left most classes feeling frustrating and incomplete, and though Azerite gear was supposed to be the replacement, it missed the mark completely. There will always be one Azerite trait that reigns supreme for each spec, meaning that the frustration of that particular loop will be unavoidable as long as the system is in the game.
Level 120 comes and goes. Island Expeditions have unlocked, but it turns out they’re not much fun, and the most rewarding versions are only accessible to premade groups. You turn to Warfronts only to realize they’re not available this week. Fine. You can always grind out better gear. Except as you do, you notice your new gear has higher Azerite requirements than your old gear, which means your shiny new items have fewer unlocked traits than what they replaced. Discouraged, you decide to roll as one of the cool new Allied Races. Except you can’t because they’re all locked behind reputation grinds.

I like his recommendations 2 level 1-20 zones to get to 20, then do all the 2nd zones since they are designed for walking (Horde: Northern Barrens, Silverpine Forest, Ghostlands, Azshara, & Hillsbrad Foothills if you need a little more. Alliance: Westfall, Loch Modan, Darkshore, Bloodmyst Isle, and if you need a little more Redridge Mtns, or Duskwood). Don't even bother with the higher level areas, too spread out. Finishing up a Monk now and I had done all these zones before the update, the running between quest and the 50% experience cap is driving me crazy.
If you love running old content for transmog items, you'll love the new legacy loot system. Whenever a player enters a dungeon or raid where they are 10 or more levels above the content, the dungeon or raid bosses drop an amount of loot equivalent to what would have dropped for a full group when the content was current. That means players could earn loot for five people in dungeons and loot for 20 people after soloing a raid. The legacy loot system also drops other gear types, like cloth dropping for a plate wearer. It's now much easier to get the transmog gear you want, and you can also collect gear for your alts on the same run.
There’s a lot of #content in the new expansion. It’s mostly locked behind a variety of gates, some of which players can’t even control. Warfronts are the best example. You might assume joining a Warfront is a simple matter of opening the group finder. Wrong! Warfronts are only accessible for a week at a time. It’s not precisely clear how often that week will come around (it’s based both on a time gate and on the opposing faction gathering resources) but, as of right now, it looks likely to be available just one week out of every four.
For reference, my previous best time abusing Method-0 in 7.3.5 was 32.4 hours(as show in the old thread). A difference of just over 8 hours; which isn't all that bad, all things considered. And I believe I made several errors along the way, which could be cleaned up in future runs. I believe that that gap could be significantly closed by using a monk's bonus, but I hate playing YMMV