As much as I loved the leveling experience, the revamped vanilla/BC character models, and a chance to actually spend time with the Draenei for once, I seriously doubt anyone's going to be listing Warlords of Draenor as WoW's greatest expansion. I think one can boil down the problems with Warlords to three issues:
A Lack of Content
A Lack of Stakes
Isolation in Garrisons
This third part has little to do with the article. Blizzard wanted Garrisons to be a core gameplay feature and not a cosmetic vanity project for people to work on, and unfortunately, they succeeded. Garrisons should have been player housing - a thing to collect stuff for to make it look cool, and maybe have some of the features of the "fun" buildings like the Gnomish Gearworks/Goblin Workshop or the Mage Tower/Spirit Lodge. The capital cities should have been the default log-out spot, and those capitals should have been Bladespire/Karabor. Enough said.
Earlier on, during the expansion, I wrote an article speculating on what the "middle tier" of Warlords would be. It was pretty clear that Hellfire Citadel was going to be the final raid (though it might have been called something else if Gul'dan hadn't taken over - though to be fair, the guy he usurped the Iron Horde from was named "Hellscream.) But I remember wondering what, exactly, there could be in-game to justify a middle raid tier. BC launched with its middle tier already available. Wrath had two middle-tiers, and Ulduar at least was heavily hinted at throughout the leveling experience (it was also announced at Blizzcon before Wrath even launched.) The entrance to the Firelands Raid for Cataclysm was already in Mount Hyjal, and while the exact location of it was a mystery, it was pretty clear after doing the quests in Kun-Lai that we'd be facing the Thunder King in some capacity.
With the Ogres in Highmaul dealt with before anything else (as the kind of intro-tier, like Mogu'shan Vaults,) there wasn't a really obvious place to go.
But there should have been.
We know that Kairoz and Wrathion (who didn't show up in Warlords, except possibly at the very end of the Legendary chain - though I didn't see him) teamed up with the Infinite Dragonflight to break Garrosh out of jail. In fact, it's strongly suggested that Kairoz is succumbing to the corruption of the Infinite Dragonflight - or even giving birth to it - as he arrives in Draenor and attempts to get Garrosh to start a Horde around which he will coalesce countless other Hordes from other timelines. Kairoz literally says he will become "infinite" before Garrosh stabs him in the throat.
Despite all of this, the meddling of Dragons is pretty much relegated to a single quest in the Legendary chain, and while it's a cool quest (that involves Chromie, by far my favorite dragon,) it's just a tiny footnote in a, frankly, small expansion.
The Infinites would have given us a reason to go elsewhere in Draenor - they seemed to have trouble figuring out what to do in Farahlon, and so they wound up cutting it, but they could have easily drawn parallels between the nether-torn Netherstorm and a time-twisted Farahlon. Not only that, but it would have given us a break from fighting Orcs non-stop.
But perhaps even more important than providing fodder for content (and that's certainly important,) is that it would have provided stakes for the expansion.
In the long run, two important things happen in Warlords. Garrosh dies, and we get Gul'dan back.
Essentially every other detail is trivial. Yes, the Draenei in this universe survive, which is great, but doesn't change the fact that our Draenei are the survivors of a massive genocide. This version of Durotan and Draka will presumably not be murdered by Gul'dan's assassins. But ours were.
In fact, even if you are willing to take this alternate universe seriously because it shows you how the Horde would have turned out if it hadn't become corrupted by the Legion, it just winds up getting corrupted anyway.
What we needed was a serious crisis. Even if the Iron Horde was supposed to be a threat to the Alliance and Horde on Azeroth (though as portrayed in-game this did not feel like the case - not to mention that the logic of it didn't make sense - the very technology that the Iron Horde had just gotten their hands on was the stuff that we Azerothians have been using and developing for thirty years - so there goes your tech advantage,) it wasn't really anything that hadn't happened before. Azeroth has defeated plenty of invading armies, and that's when they hadn't literally fought those same people before (while the Iron Horde only had Garrosh's recollections.)
I'll concede that not every expansion has to be "Arthas is going to kill everyone in the world," "Deathwing is going to destroy the world" or "the Burning Legion is invading," but at least in terms of story, Mists of Pandaria handled a (relatively) low-stakes situation in a way that made it feel personal and important.
Beating Archimonde in Hellfire Citadel is no moment of great triumph. We haven't even really killed him. And even if there wasn't this demonic pan-dimensional thing going on, it would only mean that we had once again killed someone we already faced before, only back then it was more important to do so.
Blizzard shied away from making Warlords a real "time travel expansion," for fear of having confusing plots and the possibility of paradoxes that they felt might be hard to follow. But in the long run, their solution wound up being more convoluted and deflated the stakes.
As excited as I'm sure they were to have these old characters back, ultimately a time-travel story has to be about more than just the setting. Watching the Iron Horde collapse and become corrupted before really getting off Draenor isn't really enough to make a compelling story - the original was far more interesting. But if this desire for a "pure" Horde led Garrosh to unwittingly give birth to the Infinite Dragonflight, and create a multiverse-threatening crisis that threatened to tear causality apart? That would have been a crisis worthy of our heroic skills.
I'm glad that we're going back to Azeroth, fighting an enemy that poses a real threat, and getting a break from Orcs. But it is sad to see how the potential of Warlords was only half-met. I worry that this will turn them off of the idea of time-travel as a concept and gameplay mechanic, which is sad, because I've always loved the Caverns of Time and all that mind-bending potential that the genre provides. As awesome as the Murozond fight was, I really hope that that's not the end of the Infinites in-game. We've seen their (purported) demise, but they're time travelers! We still need to see their birth!