Hear me out
After WC3, from Day One Blizzard took a path towards what we have now in WoW with the massive lore reworks and settings that are pulled from thin air. This was mainly done for gameplay reasons that offered a short term profit at the expense of long term quality. The gradual shift we've observed is that in new material, the company has slowly abandoned using original source material as an inspiration, and instead rewritten it entirely. This chaos is literally my thirteenth reason why, and it's giving laziness for me.
I'm not going to talk about much of the overall arc, as that's something that doesn't really concern me. I think the details, the themes, have way more of a bearing on creating a believable world setting.
Race lore started okay - The Alliance largely made sense, and the Horde's affiliation with the Forsaken was pushing it, but believable. The Horde never needed to mirror the Alliance in aesthetic, and part of what made it unique was this pact of convenience and internal tension. When they made the Forsaken N*zis, they abandoned this particular trait.
In terms of classes, they had mixed results. I do believe that factions should have had Paladins and Shamans locked. Very specifically, up until WC3, Shamans were actually very close to warlocks in some ways, but to write Thrall up as a character they changed that. I don't believe this was necessary, and would have made a good, unique flavor to carry over. Until TBC, Paladins were very specifically affiliated with a specific Paladin order, and this was later totally emaciated by "Sunwalkers" or whatever. In short, class lore should have been expanded. If they wanted a more general light-bender, you had priests for that.
In short, the Horde is supposed to be this faction of well-natured tribals tied up with the baggage of evil opportunists. Wether you like it or not, the classic marketing of Warcraft and WoW is that the Alliance is the "good guys" and the Horde "the bad guys". The added nuance that made this interesting and not mindlessly dull, though, was the unique Thrall-related element of the Horde before they made him Jesus. These Orcs, Trolls, and Tauren are tied up in a web of messy politics and shaky alliances that they have no choice but to accept. The Forsaken are just trying to figure their place out. They face the Alliance, whose only real division is the Imperialist sentiments vs. Classic Good Guys.
That was another missed opportunity in lore as well. We get drippings on it, but ultimately everything the Alliance does just pales in comparison to Garrosh or Sylvanas. These two were absolutely shattered into gross characters very few people now care for.
Overall Vanilla lore could have merely used some polish.
TBC - Done horribly wrong with numerable retcons pilfering the lore base. Draenei weren't even that bad to include, but should have been a neutral race "re-discovered" on Outland, who's small but fierce numbers would explain why no one on Azeroth encountered them. When Draenor was shattered, they staved off the damage in some small areas while the rest of the planet was destroyed. The game world should have reflected this. The Alliance should have gotten specifically playable Thalassian and the Horde the Goblins.
Yes, Alliance High AND Blood Elves. Why? For one, Blizzard retconned the Garithos betrayal into something more extreme than any player would have felt in WC3. Like, one rogue general is racist so two tight knit and interwoven races just agree to abandon one another? Absolutely dumb decision. Players could customize eye color in this version, and play as either blood elf or high elf.
The journey into Outland should have focused on Illidan, not the return of the Burning Legion's top leaders. The expansion could have featured defeating smaller remaining commanders of the Legion who we prevent from relaying the new connection to Azeroth back to HQ. This also reduces the player power creep in lore, giving breath to the idea that we are weak mortal races intertwined in huge cosmological conflicts. We would also see the Alliance actually experiencing some depth of internal tension in the face of a strengthened Imperial wing with the new elves, and the darker elements of blood elven society. I see no reason why Sylvanas' past would give them any desire to help the Forsaken, when Elves are equally as, if not more than, horrified and disgusted by the Undead at this point compared to Humans. Goblins enduring in the Horde would give believable credence to the idea of the Horde continuing as an actual threat to the Alliance, with their sheer numbers and unchallengable economic power.
At this point, I should say I would wish for Blizzard to flesh out Azeroth more, and maybe have given us a smaller Outland. Azeroth just feels abandoned by them, when this is your core! The Azure and Bloodmyst isles could have been the Goblin zones, and Quel'Thalas the Elven. More pressure on each faction in the opposite continent. This would actually give MORE power to the idea of making Sylvanas and Tyrande more desperate, though I don't think they should have gone full evil. Ultimately I think it would be good to establish that the factions did not closely work together in Outland, and that Illidan was ultimately defeated by Tyrande and the Alliance in a tragic ending of their story, and the Horde being responsible for eradicating the remaining Legion commanders in a bloodthirsty revenge for Orcish Slavery, and the Plague of Lordaeron. Nobility and Action for the respective factions. Ultimately can be used as a demonstration of the Horde "winning" an expansion by defeating the greater power, further projecting that they're not just a race of lucky idiots.
Wrath - Once again, a smaller Northrend. I loved the continent, but something players need to realize is that these huge swathes are created for the purposes of gameplay, yet actively shrink the social world for the player by dispersing the population. But Northrend didn't respect lore either, as like Outland, it was historically a desolate and dark place. Instead it looked quite happy in game, and I would have rather they focused on taking real world elements and aesthetically "Warcraftifying"/Tolkeinifying them, than simply copy and pasting the Nordic, Inuit, and Pacific themes. I also do not believe the players should have defeated the Lich King, but instead commanders. The expansion could end with his hallowed, echoing laughs ringing in ICC's halls as we break in, realizing that Arthas is not to be found, and is still out there. Seriously, Arthas' whole storyline was of a corrupted, fallen prince who's power is miraculously increasingly able to mirror even middling commanders of the Legion. Just killing him was a character injustice.
I am not opposed to the Death Knight class - We saw this breaking free with the Forsaken. There should have been an emphasis on their eternal fight to resist the call of Arthas. The playable races should have been Humans, Thalassian, Orcs, Forsaken, and Dwarves, only, and have unique storylines relating to the time of the Lich King's original rise. This would make them actual veterans of the third war. For a hero class, they didn't feel too powerful nor important from a lore perspective. They could have even experimented with making them a third faction of sorts, with the Light centered Alliance and Nature respecting Horde too suspicious of their ways. Keep in mind warlocks, even in Forsaken society, were relegated to the back, the lower rooms, and were often times even hidden. For this theme to appear in a faction was a slap in the face of the moral superiority of them, and the cosmology, essentially creating a path where everyone can wield whatever magic they want as long as they're mentally sound. No, this is a delicate lore choice to make, the Fel and Necromancy ultimately consumed their practicioners if they weren't the most skillfully careful.
From this point, you don't have to do an entire lore rewrite with Cataclysm. And while I supported a world revamp, the Cataclysm was a jumping of the shark in my eyes - Making everything look like lava or a battleground. Yet why not jump to the Fourth War? If you want to make a Warcraft MMO, the World Wars are a huge part, just like the classic Villains? In this storyline, the Horde and Alliance are absolutely brutal enemies still, and have no contrived faction conflict. In the political chaos following Northrend, watch the factions return home mobilized and at a peak power, attempting their shot at one another. Open up a few specific areas of conflict, just like in the Warcraft series, not this random ass pastiche of villages and forts hurling fiery boulders at one another weirdly placed across the map. Use your source material, and build upon it, don't abandon it! For player features, offer a whole host of new customizations ranging from appearance to gameplay to existing races instead of two new playable races. Flesh out, Develop what you have! I'm thinking prominence of the Burning Blade, Defias, etc.
Follow up with an expansion on the Old Gods. There is a perfect point here for them to take advantage of the manifesting chaos to make their claim, and to erupt onto the Azerothians the various smaller kingdoms and races that are no longer totally subject to the Alliance or Horde's power. Make your South Seas and Islands feature N'Zoth sending Lady Azshara and the Elemental Lords out to wreak havoc. No new class, but once again, flesh out what you have - Fourth specs for every class, and schools of magic or skill for players to specialize even further.
I'll stop here for now, forum can discuss anything after.
Timeline: WoW, TBC, WOTLK, The Fourth War, Dominion of the Deep. (I also believe expansions should have been longer with more patches because they exhaust material like it's nothing).
Here in this timeline I would see the game being in real life years around the equivalent amount of time as up to the start of Shadowlands.
Other neglected lore insights or bad retcons/post edits:
-Titans, who are severely reduced and disrespected in WoW's current iteration
-Class Lore(Um, does anyone remember Mages having literal hermeticists, occultists, and illuminati in the old class quests??)
-Cosmology(The Old Cosmology was way better for storytelling purposes)
-The Goblin Cartels, a potential large plot point themselves
-Trolls, who no longer are featured prominently as villains
-Various Spirit Factions, such as Dire Maul, which should not have been ended so easily
-Dark Iron, Blackrock Orcs, again another threat that was a very classic fantasy aesthetic pre-2010s, exhausted too quickly
-Dragons, wont even go there with that mess
-Removal of Mystery(The looming or ominous elements of old wow are just beaten down by exhaustion of material)
-Emerald Dream
-Caverns of Time/Infinite Dragonflight
-Legion, don't get me started with the Star Wars
-Lower tier Scourge/Legion covens
-The Scarlet Crusade, an aweomse villain enterprise and potential Alliance villain point totally trashed
-A lore friendly Pandaria
-Friendly/Neutral factions that could feature more prominence, why not more Tranquillen type places as well?