Well I wouldn’t say it’s the best expansion. It’s better in some aspects people give it credit for.
Why was it good? We got to see Queen Azshara and she lived to fight another day. 
I’m hoping to see her eventually in like an exp or two. Throw in some cosmic stuff as she was always heavily linked with otherworldy beings Sargeras (titan) N’zoth (old god). I could see it being a lot of fun. Not every ones cup of tea but I am down with this.
They need to go back to focusing on Azeroth first tho. Kinda heavy with all that spiritual Shadowlands stuff going on. We need Dragon Aspects making a comeback. Everyone gets a dragon aspect race to play with instant flight form. All classes get an instant flight form. 
Also the big rehash of all main cities drops. In this expansion. Building that hype. I can see it all now.
This would be the way I would be setting up the next couple of expansions. Who says GD has awful ideas?