Seriously, what's up with all the things threatening to destroy Azeroth outright?
The Old Gods seem to want to destroy Azeroth to get out from their prison within it. Algalon wanted to reoriginate the planet, which would have effectively destroyed the planet entirely and remade the whole thing, entirely to prevent the Old Gods from getting out. Now, with Algalon sitting back to observe, we had to step up and stop Deathwing from destroying Azeroth as well.
Granted, Deathwing was all tied up in the Old God's agenda, but you get the sense that old Neltharion wanted Azeroth destroyed because, ultimately, he couldn't take his connection to the planet's soil and rock, its very earth, for one more instant. Killing Deathwing almost seems merciful, since at the end he was nothing but a destroyed ruined pile of mutated flesh erupting from his elementium armor.
The destroyers, despoilers, deniers of forever
Meanwhile, the Burning Legion doesn't just want to destroy Azeroth (although they certainly do) but everything, everywhere. Between the Twilight's Hammer, the Cult of the Damned, the Legion, we deal with a lot of self-destructive or nihilistic entities in our time playing World of Warcraft. Some are world destroyers who intend to continue existing past the destruction of the world or worlds (both the Legion and the Old Gods will continue past their destruction of Azeroth), while others like Deathwing and the Twilight's Hammer seem content to die themselves in the process.
The biggest problem with this kind of evil is that it's extremely hard to relate to. With villains like Gul'dan, we may be in awe of their ruthlessness or disgusted by their malevolence, but we get a hunger for power. We can easily grasp Arthas' outrage and his having step-by-step made the wrong choices, tunneling himself into more and more evil actions while trying to turn it all around. But someone who just wants to kill everything? There's a reason that Kil'jaeden, the manipulative, power-hungry deceiver, is currently the face of the Burning Legion, because he seems less interested in wiping the universe out and more in cementing his own position.
It's hard to hate a hurricane
As of yet, Yogg-Saron has come the closest of any of the Old Gods to actually having a personality beyond simply wiping out everything and blowing up the planet, because Yogg-Saron enjoys mocking mortals. He taunts us with visions. He whispers in our minds across the breadth of Northrend. His glee as he warps minds and drives women and men to madness is palpable and defines him in a way C'thun never managed and which N'Zoth has completely avoided thus far. One of the reasons I did the Magnificent Bastard list was to highlight villains who had more approachable personalities.
Frankly, some of the new characters that debuted in Cataclysm were far more interesting to me than the marquee villain. I first came to know Deathwing through his appearances in the Warcraft RTS games and the novel Day of the Dragon -- and no matter what else you say about Deathwing, in that novel, he was a master manipulator. The Deathwing who took the form of Daval Prestor used charm, sorcery and intelligence to sway the kings of the human nations into offering him the rulership of Alterac and the hand of Calia Menethil. One shudders to think about what Calia's life would have been like had she married Lord Prestor.
Shades of black
It's possible to have a huge, perhaps even world-threatening villain who is also relatable. Frankly, both of Neltharion's children were more comprehensible than he himself. Onyxia's manipulation of the kingdom of Stormwind proved her to be an insidious, world-threatening power without any of the bombast of an "I will crack this planet asunder"-style villain. Onyxia wasn't threatening because she was going to destroy all life but because she clearly intended to control it.
The problem with villains who intend to wipe out everything breaks down into three basic camps.
- The unfathomable These guys are so alien and/or monstrous that we, the little guys with swords and staves and other implements of mass monster bashing, have no other idea what to do with or about them save resort to the monster bashing. We can't relate to them because they're simply too different from us. Yes, we understand that N'zoth wants to ruin our day, but its reasons for doing so are so incomprehensible that we don't really bother to even think about them. It is very easy for these to fall into the foil-and-forget club. So far, only Yogg-Saron really seems to avoided this, and this was because while we still didn't understand his motivations or reasoning, we hated his constant taunting so much that we just really wanted to feed him his thousand faces one at a time.
- The demented These are your insane cultists who don't care that they're working to bring about a world of shuffling zombies with no free will or a seething elemental chaos where no life as we know it can possibly exist because they're crazy. Sadly, while this is useful from time to time from a storytelling perspective, it's also kind of boring if it's overdone. Deathwing ended up falling into this camp. Although an actual motivation was presented for him in a story, it didn't pop up much in the game, so we just ended up with an image of him as a big, crazy, disturbingly fixated dragon.
- Cosmic locusts The Old Gods (and their minions) fall into this to some degree, but the real standard bearers for this trope are the Burning Legion, who march from world to world destroying everything because that's what they do. While Sargeras himself probably falls into the Demented camp, the Legion as a force currently continues on its mission of destruction not specifically because Sargeras wills it, not even because Kil'jaeden particularly cares about it, but because it's become part of its identity. A Legion that doesn't wage unceasing war on existence would simply fall apart, because the crusade has become what it is and what it does.
Sometimes you just want to punch a jerk
Arthas/The Lich King had issues with presentation for some people, but there was no doubt that he was a threat to all life on Azeroth and that people had real, personal reasons to want to kick down the door to his citadel and go feed him his teeth. He compensated for the distance of his motivations with personality and menace and personal interaction with the players.
As we move into Mists of Pandaria, we'll meet a host of villains whose goals range from the seizure of ancient power and rulership (the mogu) to the embodiment of destructive emotion (the sha) to the biological need to expand and devour (the mantid). Due to their natures, many of these enemies are inherently personal even as they go about their schemes and plots -- the sha threaten not to destroy the world itself, but the inner world of all they encounter, drowning everyone including you in dangerous emotional imbalance -- and none of these villains stands as a central figure seeking to annihilate everything. (Well, so far at least.) I think this is a nice change of pace. We've saved the world a few times now, balked Algalon, stopped Arthas, destroyed Deathwing the Destroyer -- it's time we get our feet grounded again.
While you don't need to have played the previous Warcraft games to enjoy World of Warcraft, a little history goes a long way toward making the game a lot more fun. Dig into even more of the lore and history behind the World of Warcraft in WoW Insider's Guide to Warcraft Lore.