I know many player, myself included, wanted to fight the Legion in this expansion (before WoD was officially announced). But I think Blizz did a great move to make us hate the Legion even more.
We get to go back to a pre-corrupted Draenor and see the land in all its beauty--before the Legion corrupted the orcs which eventually leads to war and the destruction/creation of Outland. Just looking at the concept art and recently released gameplay footage of WoD has blown me away. I think Shadownmoon Valley and Temple of Karabor can be the nicest zones Blizz have ever created. I'm going to boost an ally to 90 just so i can play in that area.
Because we get to see Draenor as it once was, we should hate the Legion all the more for destroying this gorgeous world. Outland is a desolate wasteland compared to the beauty of Draenor.
So overall, good move Blizz in letting us see a world before the Legion has corrupted its inhabitants and destroyed everything. When we do finally fight the Legion we should hate them all the more because we've seen a (one of many) beautiful world that they've destroyed. I think this expansion will make the legion themed one even better.