Name any character established in Warcraft 1, 2, or 3. Examine their characterization, pre-WoW.
Compare to WoW characterization; a particularly notable example is Kael'thas, who, in WC3, just wanted a safe home for what remained of the 'high' elves, while in WoW was pretty much an 'Imma-kill-em-all' Maniac.
(To clarify: Kael'thas was formerly the prince of the Blood Elves. He genuinely cared about his people and traveled to Outland in hopes of finding a new way to sate their magic addiction. Come The Burning Crusade, when the rest of the Blood Elves travel to Outland, they find that Kael has allied with the Burning Legion and is capturing the Blood Elf pilgrims as slaves. As of patch 2.4 he was 'upgraded' to a raid boss who was attempting to summon Kil'Jaeden, last lord of the burning legion, to destroy the world.)
Edit: A convenient bullet-pointed list, additional snark in <> brackets.
* Previously powerful, important and charismatic characters being reduced into the role of an Evil Overlord without any personality whatsoever. See Character Derailment. <Or see above at the earlier comment regarding Kael'thas>
* Continuous sloppy changes to the continuity. See Retcon. <Way too many changes; notable ones include Draenei entirely, blood elves left in quel'thalas after the events of WC3, and Arthas allegedly keeping all the undead 'relatively' docile with what remained of his humanity, despite it being pre-established that he had forcibly yanked his humanity OUT and kicked it to the curb.>
* The formerly story-driven world being changed into a static place with only few permanent changes. See Status Quo is God. <Cataclysm chages this after nearly 7 years of stagnating like a brackish pool of swamp water, but only geographically.>
* The villains suddenly being incredibly impotent despite the fact that their only true enemies are also feverishly fighting each other in the side of the good-evil conflicts. See Villain Decay. <See: Arthas in Wrath of the Lich King. Any other Major figure in Warcraft that you fought and wasn't murdered by the end of the game, and probably a few that were *Cough*Cho'Gall*Cough*>
* The Warcraft tabletop RPG and computer games always seem to conflict, causing their fans to dismiss the other as non-canon. <I have nothing to say about the tabletop system, as IIRC, it's a white-wolf system, and therefore 'meh' at best.>
* Every Warcraft fan (or detractor) ignores great chunks of lore, depending on how he sees the universe. The lore's a mess, to state the obvious. <Mess is an understatement; It's a tangled knot of christmas lights that only gets more tangled every time you pull on one line, until you get fed up, pitch the whole mess, and buy new lights. Which immediately get merged into the tangle via some sort of horrible osmosis.>
* In many ways, the gameplay of World of Warcraft is completely at odds with the story - for example, in Wrath of the Lich King, the Horde and Alliance are allied against the Lich King, but you can still fight the opposing faction in various PVP modes, as if the Horde and Alliance were still at war. <Can be explained away as 'show-fighting'>
* Some fans refuse to acknowledge anything written by Richard A Knaak. <Technically good, but you want to throat-punch all his characters. Repeatedly.>
* Most Horde players hold that Thrall is still Warchief. Garrosh is merely keeping his chair warm while he keeps the world from collapsing. <I have to agree with this one; Thrall is far more awesome than any other Orc, by merit of having more than 10 synapses to rub together.>
* Some fans also outright refuse to count the comics as Warcraft canon. <Personal note; Considering the comics introduced me'dan, the biggest mary-sue character this side of the original Mary Sue, that's a damn good decision>