Yes people were excited to explore it during Cataclysm. And what we ended up getting was a weird parody on Indiana Jones, Hitler, and nazi's. It was disappointing as hell and pretty much everyone I know these days goes to Hyjal for 80-85.
I loved Pandaria, I love Legion. Yes Illidan visited the Tomb of Sargeras, as did Gul'dan and I think Gorefiend, but none of them ever made it to the Tomb's number one treasure: Sargeras' actual physical body. We've known it's there, and now we're finally going in to see it. How is that not exciting?
The entirety of Warlords of Draenor has been a build up for this expansion. Warlords of Draenor was not about Garrosh or about the warlords of Draenor. It was about watching Gul'dan and the Legion conspire to make their plans come to fruition. Legion is the culmination of that.