It’s a good thing that the previous expansion, Legion, was the best in the game’s history because Battle for Azeroth is coasting on its success. The major class redesigns that happened then remain in effect (though some are a little worse, and some a little better), and the combination of World Quests and Mythic+ dungeons means there’s always something to do, no matter your skill level or how long you can play.
Lightforged draenei - "For untold millennia, the Army of the Light waged war against the Burning Legion throughout the Twisting Nether. The draenei most committed to their long crusade would undergo a ritual to become Lightforged, infusing their bodies with the very essence of the Holy Light. After finally achieving victory on Argus, the Lightforged Draenei have undertaken a new mission: protecting Azeroth from rising threats and helping the Alliance push back against Horde aggression."
Kul Tiran human (8.1.5) - "Kul Tiras was founded by fearless explorers who sailed uncharted waters in search of adventure. As a key member of the Alliance of Lordaeron, the Kul Tiran navy dominated the seas of Azeroth with its legendary fleet. But after years of turmoil and hardship, the kingdom grew isolated and vulnerable to dark influences. Thanks to the help of brave heroes, House Proudmoore has been restored and Kul Tiras is poised to fight alongside the valiant Alliance once more."