I've been a big Warcraft fan since long, with Warcraft 2 being my first Warcraft game. Suffice to say, the lore has changed alot. Some changes were minor and inconsequential, and others have a profound impact on how prior games are meant to be viewed in the context of new lore. There are many changes and inconsistencies; retconning of Orcs that has happened more than once, the Draenei, entire Wrath of the Lich King, Warlords of Draenor and so forth.
My biggest issue with Legion from a lore perspective is how Illidan is treated as a Hero, and that we were wrong to end his reign in Burning Crusade. Yes, I don't mind that Suramar looks nothing like the WC3 Suramar or minor stuff such as that. By comparison, they're very trivial.
Let's go back to Warcraft 3 for a moment, because WC3 is clearly the most influential game in the series in regards to how it influenced the lore of WoW. WoW is based more on WC3's lore than the prior games (which is natural.) In WC3, a strong theme is the preservation of honour, and how you can never allow the situation to dictate your methods. For example...
The Human Campaign is about how Arthas defends his homeland with such zeal that he ends up sealing its doomed fate. He says "I would gladly bear any curse to save my homeland." One pivotal moment is when Arthas decides to essentially raze the city of Stratholme to the ground to prevent them from becoming part of the Scourge, a method that Uther and Jaina reproaches. Finally, when he picks up Frostmourne, he is indeed able to slay Mal'ganis, but he also becomes a pawn for Ner'zhul.
The Orc Campaign is about Grom Hellscream and his redemption. Thrall stands for the "New Horde", whereas Grom Hellscream is a remnant of the old one, the reminder of the past which plagues the orcs. Like Arthas, he gives in to the situation; When Cenarius threatens to destroy the Horde's operations in Ashenvale, Grom chooses to drink the blood of Mannoroth in order to fulfill his mission. He succeeds and kills Cenarius, but he becomes a pawn of the Legion. In a final act of what would become his redemption, Grom refuses to acknowledge that he is as bloodthirsty and vile as Mannoroth. He strikes down the Destroyer in what was a selfish act, but in doing so redeemes the Orcish Horde as a whole.
The Night Elf campaign, finally, deals with this discussion in the story about the Stormrage Brothers. Each of them vie for the affection of Tyrande Whisperwind, but go on about it in wildly different manners. Illidan Stormrage, a demon hunter, would go to any lengths to defend the elven lands from the Legion. In the only mission in which you control Illidan, he picks up the Skull of Gul'dan and absorbs its powers, becoming much like a demon to the point where Malfurion mistakes him for one of the Legion's servants. Illidan achieves what he was set out to do; he destroyed Tichondrius and according to Kil'jaeden "secured the downfall of the Legion at Hyjal", but he is banished by Malfurion for what he has become.
His storyline continues in the expansion, the Frozen Throne. The main part of it is Illidan, and how he goes to any lengths to save himself from punishment by Kil'jaeden. He is ordered to destroy the Frozen Throne, and he bears no qualms about using Naga to kill innocents as he pursues the Eye of Sargeras. Another piece of dialogue helps highlight the differences between the brothers:
Malfurion: "Too much blood has been spilled on your account, Illidan. Even now I can feel the lands of Northrend reeling from the spell you cast. Imprisonment will not be enough this time."
Maiev: "I will execute him myself."
Illidan: "Fools! Can you not see? The spell we channeled was meant to strike at the undead, our common enemy! My mission was to destroy the Lich King's stronghold of Icecrown!"
Malfurion: "At no heed to the cost? Because of you, Tyrande is dead!"
An interesting thing is also about how the Night Elf campaign also reflects this theme not only in the character of Illidan, but also Maiev. At the start, we sympathize with Maiev because she is right in bringing Illidan to justice given what he does in the earlier parts of the campaign. Towards the end, however, she becomes obsessed with the hunt, even going so far as to lie to Malfurion about Tyrande being killed just to keep him focused on capturing Illidan. From this point onwards, Maiev is portrayed in a villainous light just because she went too far.
In Warcraft 3, Tyrande gives her final answer to Illidan:
Tyrande: I was wrong to set you free, Illidan. I can see that now. You've become a monster.
Illidan: Monster? Is that what you think of me? I have always...cared about you, Tyrande. I sought only to prove my worthiness--my power!
Tyrande: Raw power is no substitute for true strength, Illidan. That is why I chose your brother over you.
Even World of Warcraft reiterates this theme in what I find to be the iconic words of Saurfang in Icecrown Citadel:
"Honor, young heroes. No matter how dire the battle, never forsake it."
Given this theme, it seemed in my opinion appropriate that Illidan would die as a villain. At the end of the Frozen Throne campaign, he is bested in combat by Arthas and once he wakes up, he has gone insane. In World of Warcraft, Malfurion tells Remulos:
"Illidan sits atop his throne in Outland – brooding. I'm afraid that the loss to Arthas proved to be his breaking point. Madness has embraced him, Remulos. He replays the events in his mind a thousand times per day, but in his mind, he is the victor and Arthas is utterly defeated. He is too far gone, old friend. I fear that the time may soon come that our bond is tested and it will not be as it was at the Well in Zin-Azshari."
So the end of Illidan's story-arc prior to Legion was that he ended up insane and alone atop of the Black Temple, ruling over a dead world which Kil'jaeden called a "forsaken backwater." His mad reign had to end. He had gone too far, like Arthas and like Maiev. A tragic tale all in all that was consistent with what Warcraft was about.
Then we get Legion.
Suddenly, Illidan is no longer dead. (This is a problem that has marred Warcraft lore since long, and I blame that on the poisonous comic-book influences that the writers seem to draw upon.) Not only is he dead any longer, Xera (which is supposedly a part of a naaru prime) tells us that us killing Illidan was the "ultimate betrayal." We were the bad guys. Not him.
Okay, first of all, this is very strange from a lore consistency standpoint. WoW lore has never been consistent, and it's always been a problem. It has never been able to seemingly expand upon a subject without altering its core meaning in some sense. But this goes beyond the normal inconsistency - it undermines one of the most prevalent themes in Warcraft.
Now, A'dal was really a bad guy for leading the siege against the Black Temple. Now, Akama is a bad guy because he mistakenly lead a rebellion against a tyrant. Lady Vashj was really a good guy when enslaving Broken in Zangarmarsh, because she was per extension helping the cause of Illidan, who is now a hero. These inconsistencies has been explained by fans saying it was all based on "miscommunication," that we did not know that Illidan was arming up against the Legion. (This is also a strange idea, as according to Malfurion, Illidan was mentally broken beyond repair, probably to the point where he would no longer be composed enough to conceive of such a long-term plan. In fact, he is even talking to a skull when we find him in Black Temple, which isn't the sign of a healthy state of mind.)
Still, this isn't true - we always knew there were a difference between the Illidari demons and the Burning Legion themselves. There was even the Fel Reaver raidboss outside the Black Temple that had been sent there to kill Illidan. In fact, what Illidan was doing (back then at least) was that he was arming against the retaliation of Kil'jaeden, as he'd failed to uphold his end of the bargain. Other than that, he was just ruling over a dead world. There was nothing altruistic about his actions. He even sent the Scryers to lay waste to Shattrath City because they posed a threat. Truly, had he been this good guy, wouldn't it have just been simpler to send a letter to A'dal explaining everything? And this doesn't even take into account that Xera, another naaru, could've just told A'dal that what he was doing what wrong, which makes the idea of "miscommunication" seem quite mundane and stupid.
I mean, given this theory, I do think it's a damn shame that we didn't just talk to Illidan. Sure, he was mad and power-hungry and everything, but imagine what a force the Black Temple guys would've been! Teron Gorefiend, The Reliquary of Souls, that infernal boss... would've been a pretty cool thing to have! I mean, who cares what damage they wrought or how malicious they were? If it means the Legion's destruction, it's probably ok.
This puts an even more troublesome thing to light; if everything Illidan did during his tyrannical reign of Outland was justifiable because it served to destroy the greater evil, then we must come to the point when the Legion will end up good guys. Of course, we don't know that (yet) but what will happen is that Sargeras created the Legion to fight the Void Lords.
Then we get into the miscommunication argument again; surely, in light of this revelation, everything the Legion did is morally justifiable. If destroying worlds and siphoning World Trees helps the Legion grow in strength so that they can fight the Void Lords, it must be alright, no? Because, at the end of the day, destroying the biggest evil must always be the biggest concern, no matter the method. That is what Xera tells us. That is what the new Legion lore tells us. So when we get this information, that the Void Lords are the bigger threat, then Tichondrius, Mannoroth, Archimonde and Kil'jaeden will be all good guys. Everything they did was to work towards this end. Now we've also come full circle; Illidan was a bad guy because he didn't know that everything the Legion did was to fight the even bigger baddie!
Even if this theory of Sargeras vs Void Lords turns untrue, i.e the Legion were doing all this for no real reason other than to have fun, it still points out the flaw in this line of thinking. Everything a character does is morally justifiable so long as there is a bigger threat.
Now, am I saying that there should only be one way to do things? One character is always right, the other is wrong? No. But a universe should always be thematically consistent, and the themes arises out of a writer's intention. In WC3, that theme and the intent of the story is very prevalent and clear. Still, I think there always -was- an interesting ambiguity in the Illidan case. When Illidan destroyed Tichondrius, he effectively saved the world according to Kil'jaeden, but he also paid the price of effectively becoming a demon himself. Was it a price worth being paid? Now, we're -given- that answer. According to the new Legion lore, yes, definitely. Malfurion was just being an asshole 'cause he didn't understand nothing. So was Tyrande. Akama. If anything, the new Legion lore removes the interesting things about Illidan. Malfurion was just a conservative asshole. Illidan was the glorious hero we all failed to misunderstand. It feels like it's fan-fiction at this point.
But that's what it is, isn't it? People wanted Illidan back. They weren't happy with how his death was dealt with in WoW, even though his story arc was done. So, we got Illidan back. And now he's a hero. Even though it stands in stark contrast to previous lore.
EDIT: I will say that I'm praying that Xera turns out to be some form of Kil'jaeden deceiving us or the Void Lords or anything. If I get that, I'm fine. I'd even commend Blizzard.