By adding them as a playable race they lost pretty much all of their mysteriousness that made them special in the first place. I'd rather have seen them as an NPC faction instead too.
It feels like the lore got raped a little bit... again.
You do realize this whole expansion was pulled out of Blizzards ass right? There is no lore supporting any of this except the one Pandaren in WC3.... You do realize this?
Where else is lore supposed to come from if not from Blizzard? Should they create expansions from fanfics? They may tread on butthurt lorejunkies here and there and everywhere, but that hasn't ever stopped them.
As for the argument that lore shouldn't be exclusively represented in books - I can certainly understand that.
However, I can only think of a certain number of things to adress that problem.
1. Don't do novels at all
2. Implement the events of the novel into the game
3. Write novels that are irrelevant to what happens in the game
As for 1, obviously a bad idea. People want Warcraft novels. And there are certain stories best told in novels. In WoW you play your character, the story focuses on what YOU do, and even if there are certain important lore characters here and there, mainly you're interacting with all kinds of different characters throughout the whole world, and the appearance of major lore characters should be rare, so it still feels special. Novels focus heavily on certain lore characters. You get a better understanding of those characters through the novels.
2. That's probably what most people feel is appropriate, and I would have no problem with it. Except that it's hard to implement the story of certain novels, like the shattering, or tides of war, and it would take up an enormous time to do so. It would come at the expense of other content. The best we can get in that regard is scenarios like the theramore scenario.
3. Novels like the first three, or the war of the ancients trilogy. They all deal with things that happen way before WoW, so they don't need to be represented ingame. But Blizzard has shifted from doing those kinds of novels to focusing on major lore characters, Varian, Thrall, Arthas, Jaina, Malfurion, Vol'jin, for exactly the reason I mentioned above. WoW is our story. The story of our characters. That's why most city leaders did nothing for the first few years of WoW and still don't do very much. I want them to keep writing novels about those characters. They do a great job of connecting those characters in the novels to what happens in the game. And they do a good job of portraying those characters and writing compelling stories. Ideally I would like some stories that focus on past events like the war of the ancients every now and then. For example I think a novel about Shaohao would be great. Maybe once they've gone and dealt with most faction leaders we can see more of that.
As for the lore books in game, they really can't replace novels, they're like small summaries of what happened in the past that take like 1 minute to read.