Yea what they did to Arthas is almost insulting. They ruined the last remaining embers of the WC3 storyline.
I was hoping for a big reveal during shadowlands. I dont know if you ever heard about the theory that Anduin is actually the son of Arthas. Things kinda add up timeline wise, also Anduin looks a lot like Arthas and nothing like Varian. And ofc a priest with a warrior father makes less sense then a priest son with great affinity to the holy light with one of the greatest paladins ever.
Ofc Arthas fell from that high horse but they even redone the cinematics with Anduin - you cant miss the paralells of Anduin marching into “Undercity” vs how Arthas walked back into his home before he killed his father.
And even in the new cinematic we see the recall for the posture of Arthas in Anduin as he raised his sword against Thrall.
Anduin also looks more and more like a paladin and not like a priest since BFA.
I truly hope they will stop making him cry soon, it was enough times we seen him crying …sure he has Ptsd now and we might get 1-2 more cinmetatics with him in tears but I think most of us would love to see him “man up” get his sh*t together and become a true leader. And I’m saying this as a mainly horde player.
They missed a huge opportunity for his character development by killing off Arthas and turning him into 30 anima…
if they would have had the balls to reveal Arthas was his father and they built a story on that where in the crucial moment the memory of his real father and his deeds would have given him the power to resist going down the same path would have been awesome. Or even see him fall would have been better than what we got but I think repeating the same fallen hero arc would have been boring. People love to see heroes that struggle but manage to overcome their issues in the end and do the right thing.
Without Arthas present the whole thing would be less impactful but they could still give us this “twist” down the line with Anduin and I think it would be awesome.
I also love the weapons that have a “being” trapped in them and they talk to the wielder. This bring me to the Ashbringer one of my all time favourite weapons and its corrupted version with its whispers. It was truly awesome and chilling to hear the blade whispering snippets of truths when you know the story of the blade and the story of the family that its tied to.
Also the fallen naaru core lore was awesome purified by the light when they attempted to destroy it thinking its a sort of weapon or tool of the darkness 
The lore became terrible, Danuser should have been fired years ago because all he did is he ruined the great stories and character of the past we loved and gave us terrible new ones and stories that led to nowhere and made no sense.
The one think I liked the most in the shadowlands lore is when Garrosh stood his ground, he regrets nothing, goes out like a boss and disenchants himself not willing to be part of that terrible expansion anymore! 
Also its crystal clear the Primus was supposed to be the actual Jailor. Zovaal had domination runes in his body …they changed the plans and cut a full patch cycle so we didnt get to see the true Jailor …but they even left in hints everywhere like the desription of the Primus and how he never lost a fight
yet we suppose to believe he was defeated by Zovaal and chained for millennia… not to mention we later see the Primus making a fake “jailed” Primus clone in his place so that fake version could craft the legendaries for us…
And ofc the ending of that expansion made 0 sense we just got a vague threat of something bigger evil that the a cosmos devided cannot withstand… so from what we know Zovaal could have been even right and I see a redemption arc coming for Zovaal 6 expansion later 
And what they did to Sylvanas is just terrible. Her soul was split but it was suppose to be her anyways …and that how she ended up being manipulated and “serving” the same way is not even funny…
But Dragonflight lore is pretty bad too…
We are killing primalists left and right when we know as the “champion” that the titans are controlling the flights they influenced with their “special order water” transforming them. And that the primals are the actual children of Azeroth… so who are we fighting against?
Its clear from the info we gathered ingame that the Titans are not the good guys at all…
And its funny after you finish Aberrus and see old God minions and void you go to speak to Alexa and you dont mention anything and Wrathion and the other black dragons dont tell her about this old God/void problem either so she is happy to send you over to the greens to help them with their gardening 
Or how he forget that all this “oathstone” “shadowlands five covenant 2.0” led nowhere because the dragons were empowered by Azeroth and not by the stones …not to mention Elune already “lifted” up Kalec to be the aspect during the ritual…
But hey no one cares about the masses we murdered for nothing while we were on the quest to restore the oathstones which did nothing in the end 
awesome writing…