Legion has got more subtle little treats for people paying attention than any previous expansion. There are things like all the special emotes and even actions that you can find with different artifact weapons as well as tons of hidden treasures and other such things.
But this is the subtlest.
On my Night Elf Demon Hunter, I noticed that when I was in Valdisdall, the little Valarjar settlement where the quartermaster is, Havi's ravens Huginn and Muninn (straight out of Norse mythology) would emote that they don't seem to like me for some reason. I assumed this was the case with all characters and I'd only noticed it on him.
But then I was doing the Rogue class campaign on my Undead Rogue and came across a readable item found on the Nagalfar (the ship in Maw of Souls.) It tells a story of how Ravencrest tricked those two ravens into giving him a magical artifact. The two birds are consumed with a total hatred for Ravencrest and his entire people, aka the Night Elves.
If I didn't play a Rogue or a Night Elf, I would never have noticed this.