Warmode is one of the real stand-out features of Battle for Azeroth, even if it is a somewhat controversial one. Warmode tries to revolutionize world PvP like the game has never seen. By switching on Warmode, you enter a new version of your server with only other people looking to fight out in the world. The result is a more volatile world where fights can break out at any time, and groups from to go fight the opposing faction.
I highly recommend actually staying in the 20-60 range zones until you ding 62. The reason for this is that despite getting a slight penalty in experience for being over-level, the advantage of having flight will more than offset this. That, and WOTLK and TBC zones are the slowest part of the leveling process. Minimizing your time there as much as possible is worthwhile.
-New dungeons- About 3/4 are fairly decent, not too long not too short, but none of them are compelling, none make me say to my friends and guildies, "Hey, let's do this instance, I love the theme and encounters." They're dull but tolerable. The other 1/4 of the dungeons just aren't fun and you will groan when you get a mythic Keystone for the Underrot, the snake temple, or Waycrest Manor. Waycrest Manor is actually one of the better dungeons, however, with the new Infested affix, Waycrest Manor suffers from many game-breaking bugs that end in the entire instance being pulled due to doors not properly working as intended.
New to Patch 8.1 is a new leveling flask called the Draught of Ten Lands which increases all primary and secondary stats by 20 and experience gained by 10%. This effect lasts for one hour and persists through death, similar to other battle flasks. This item can be purchased using a new Patch 8.1 currency called 7th Legion Service Medal or Honorbound Service Medal which can be earned doing the new incursions and Warfront activities. Simple earn these medals on your main character, purchase the flasks, and send them to your other characters. The cost is 10 of the medals.
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 monk...so...yeah. YMMV