Indeed, the Legion, the Old Gods, and the titans are the great over lying plot, the brooding destruction that overshadows the realm, and that is all great and enthralling. But, and I mean this as a major but, at the heart of it all is nations who don't get along, small alliances that fracture in an instant. The very mortal nature of a species is the self destructive pattern that all civilization inevitably boils down to. Inner turmoil, that is the heart of Warcraft. Not the next great evil to stomp on everyone, it's how the races deal with it, or rather squander amongst one another to deal with it.
If you have your reservations then think of this: Why are the Blizzard team so eager to return back to the old ways. Why send Thrall away and replace him with a warmonger, why build the prejudice of Wrynn to such an extent that war seems inevitable. The Southern Barrens is in open war, as is Ashenvale, as is Andorhal, and Gilneas, to name but a few.
Open war has finally arrived. Vanilla had its long wavering truce, TBC had Shattrath, and Wrath had the warfront against the Lich King, but now everything seems forgotten, mostly due to the likes of Hellscream and Wrynn. Legion or not, this is as much Orc vs Human as ever, and Blizzard is putting it on the forefront, as it should be.