These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Here are the subjectives found in Warcraft series.
Base Breaker: Varian Wrynn and Garrosh Hellscream are the two most prominent cases, one for being an angry post-Literal Split Personality with one half being a slave to Orcs for quite some time, had his home destroyed by the orcs and his father betrayed by one even earlier and rather expectedly, is none too happy about them, while the other is a racist war-promoting bastard of questionable leadership skills taking over from the level-headed, peace-seeking, Thrall who somehow was a Emo Teen beating himself up barely a few years ago.
Canon Sue: There's a very simple, one-question test to determine whether a character is a Canon Sue: "was this character created or popularized by Richard Knaak?" You'll only ever be wrong for the few characters that reached Canon Sue status without Knaak's help.
Fortunately, their Sueness doesn't really transfer into other media. Several of them were added into World of Warcraft but play fairly minor roles, even though Rhonin is technically a key person as the leader of the Kirin Tor. But even in the Ulduar trailer, his role is fairly passive compared to Jaina and the others.
Goes so far that Knaak often gets blamed for characters he didn't create (such as Med'an).
Metzen's pet Thrall is considered a Sue by many people. He has so many powers and titles that it's almost impossible to list them all. At one point, it was even mentioned that he would be taking the Black Dragon Aspect's title and powers. He did, in a way, but he is just the Earth Warder, not an Aspect. Thrall, at the moment, is a God-Mode Sue if there ever was one.
To be fair here, Thrall wasn't that bad in the RTS series. It wasn't until World of Warcraft's Cataclysm came around that Metzen felt compelled to start shoving Thrall down the fanbases throats anytime new lore came around; even in scenes that are suppose to be Alliance exclusive.
To enlighten and elaborate, Thrall's Canon Sue title generally falls under factional and philosophical divides. Being a Horde character that tends to be Only Sane Man when it comes to constant self-harming strife in the series, you'll usually find the people most critical of Thrall to be Alliance-playing players. Even then, it tends to be split between those who want to keep the War in Warcraft, and so object to a peace-promoting leader being so successful, and Alliance players who want peace but resent the fact that the leader of the Horde gets to be the mouthpiece for it. The latter actually tend to be more vehement about it: seeing someone from the "other side" being rewarded for his attempts to ensure peace while anyone attempting peace on their side doing the same is either killed off or given a Trauma Conga Line, can understandably cause a little bit of jealousy.
Cliché Storm: Every line that doesn't contain a proper noun, you've heard in some other fantasy work. This is particularly noticeable in Reign of Chaos.
Gul'dan is a power-hungry orc who voluntarily corrupted his people into a bloodthirsty horde which he secretly controls, planned the draenei genocide and brought the orcs into Azeroth so they could trigger two wars. He also created Garona as a "breeding experiment" between an orc soldier and a female draenei prisoner, after which she was magically aged, tortured and mind controlled into becoming his personal assassin. Finally, he betrayed the Horde to follow his own goals, which caused the defeat of the orcs. Even after his death his evil lingered around his skull, corrupting everything around it.
DoctorTheolen Krastinov in Scholomance, known by his victims as The Butcher, subjected his victims to painful tortures to devise a plague, keeping them alive for weeks from wounds that should have killed them on the first day. When he was finally done with them, he brought them back from the brink of death so he could throw them to his ghouls, laughing as they were eaten alive.
Deathwing the Destroyer, the ruler of the Black Dragonflight, formerly known as Neltharion the Earth Warder, is one of the most ancient villains in Azeroth's history and one of the most monstrous. Deathwing possesses genocidal hatred directed towards anything that isn't a black dragon and has tried many times to exterminate all else that lives. Deathwing tricked his fellow dragonflights into binding their powers to a relic known as the Demon Soul and proceeded to depower his fellow Dragon Aspect and drove the blue dragonflight into practical extinction, gloating all the while. He raped his former consorts and due to his gaining a unique body of molten fire, only one survived, hideously scarred. He was responsible for the capture and forced breeding of Alexstraza, letting her beloved children die and all the while planning to steal her eggs and corrupt them. Deathwing unleashes the fullest measure of his evil in Cataclysm when he initiates events that cause countless deaths and occasionally attacks areas by burning any living thing he finds. Not even his own "superior" Dragonflight is exempt from his plans, as he is hinted at creating the Twilight Dragonflight to replace the remnants of his own.
And speaking of the third game again, the sung part at the end of The Frozen Throne ending cinematic. No wonder it was reused (with a different voice and lyrics) in World of Warcraft: Wrath of the Lich King.
Designated Villain / Informed Wrongness: While Illidan did do a lot of amoral things, it's still hard to understand why exactly Malfurion decided he had to be banished for turning himself into a demon, even though all he did after becoming one was, you know, saving the whole Forest.
Foe Yay: Maive Shadowsong, Illidan's former personal jailor, seriously comes off a lot like a spurned Yandere during her pursuit of him in the events of The Frozen Throne.
Game Breaker: In III, a high-level hero can often handle entire maps by himself, especially if you've been giving all the stat upgrades to one guy.
Frozen Throne's Orc campaign basically gives you a new Game Breaker every time you kill a new monster. Here, have a shield that boosts stats while setting enemies on fire, or a hat that shoots lightning, or a stick that summons reinforcements while making your allies go faster, or a free Chain Lightning spell, or a healing item that amounts to a fountain of health following you around...
Hilarious in Hindsight: Remember when Arthas said "What trickery is this!? Mal'Ganis! I don't know how you survived..." and later, after encountering Muradin's dwarves, "Doesn't anyone stay dead anymore?" It's funnier to think about it after some characters are Back from the Dead in World of Warcraft :Muradin and Mal'Ganis themselves, Kael'Thas...
That particular example also counts as Hypocritical Humor, since Arthas is the one who got them all killed (or tried to) in the first place.
The Leeroy Jenkins meme that was born in World of Warcraft makes the third Orc mission even funnier. Grom Hellscream was Leeroying it out for years before Leeroy Jenkins.
Arthas massacring Stratholme so the city does not fall to the Undead is one In-Universe, but highly contentious amongst the players, with lots of arguments resulting over the finer details (the fact that the Plague can not be cured vs. the morality of the Mercy Kill, how quickly he leaps to this idea, etc).
Hiring mercenaries to help him burn the ships so his rebellious soldiers cannot flee Northrend and escape his obsessive quest to find and destroy the source of the undead, then telling the men that the "foul beasts" had done it all, is a lot less contentious of one.
Wandering off into the wilderness after claiming Frostmourne and leaving his former soldiers to die would probably be one if he wasn't already having his mind stolen by Ner'Zhul.
Ner'Zhul himself crossed it after Warcraft 2, when he abandons the Horde for himself, opening countless portals across Draenor in an attempt to escape to new worlds, which ends up tearing the Orc homeworld apart (and unintentionally sending him straight into Kil'Jaeden and a Fate Worse than Death).
The dropping of a mana bomb on Theramore is this for Garrosh.
They also changed the novels accordingly by giving them the World of Warcraft icon even if the stories take place during the RTS games.
Narm Charm: The writing in Warcraft games and books comes across to many fans as cheesy, but many of them enjoy the series specifically because of that.
Sturgeon's Law: The enclosed "World Editor" allows a creative player to create their own scenarios and maps for the game with a great deal of customization options. Unfortunately, many of them suck or are knockoffs or endless rehashings of the same type of map. Or all three.
The "Spirits of Ashenvale" mission of the first orc campaign where you have limited resources and are tasked with harvesting huge amounts of lumber with the worst lumber gatherer in the game. The only gold available for mining is far away from your main base, so you need to raid enemy bases (and the units that are good against buildings are bad against units). Your unit options are limited to some melee units with an inefficient anti-air attack, the worst ranged unit in the game, and the enemy just loves attacking your harvesters with air units, and most damning of all, no way of healing your units. There is a way to get lumber faster, but it involves a ridiculously difficult battle against tough enemies, during which you will take heavy losses, which must be replaced at great cost. And adding insult to injury, the hero you start with is The Berserker, and this entire mission (defending against impregnable bases) goes against everything he stands for.
The chapter right after that, "Hunter of Shadows," isn't anything too difficult per-say, but its well known to be problematic just to get passed the opening battle where you must survive Cenarius' all-out assault with nothing but your berserker hero, and a few other units that are likely to die off fairly quickly. Its more of a race to get a decently sized force, then to actually win against the assault with the small force you have currently.
The expansion gives us the first undead mission "King Arthas"; especially on Hard mode. Despite having practically unlimited resourcesnote 120,000 gold and lumber split evenly amongst you and your two allies, and three factions to control, the game-play to complete the mission is an absolute freaking nightmare! You have to block off three map exits with each of your three factions in order to not allow a certain number of humans to get by and escape Arthas' slaughter. And while you do that, you gotta destroy 9 outlying villagesnote 3 for each of your factions that stop these humans from spawning. To top it off, there's a Paladin encampment in the center that not only protects these villages if they are attacked, but acts as a barrier to keep each of your three factions separatednote Sylvannas can handle the Paladin on her side just fine thanks to her Silence spell, but Arthas and Kel'thuzard's sides have no real way to counter them. To top it off, your forces are vastly limited to 40 between each of your three factions for a total of 40/40/40, and aside from Ghouls, you're restricted to Abominations from Arthas' faction, Necromancers from Kel'thuzard's faction, and Banshee's from Sylvannas' faction. Don't be surprised if you find yourself having to resort to cheesing the village structures with Arthas' Animate Dead.