Vast majority of players are just excited for more content.
As with most expansion reveals, the theme of the new expansion is going to be "take it or leave it", but even if people don't like the theme they'll probably buy it anyway just to keep playing. A lot of people hated the theme of MoP or the premise of WoD, but enjoyed the content anyway.
The people who are into the story hate Sylvanas and want to move on from that story as quickly as possible.
Warcraft 3, WotLK, and Death Knight players are especially offended that the LK got worfed by the worst character in the story.