*LORE SPOILERS AHEAD*

I have mixed feelings about this new expansion myself. Vanilla WoW is getting a makeover, the old world will be forever changed. A lot of people say that Blizzard is destroying the Warcraft lore with this expansion. I say both "yes" and "no" to that statement. Let's not forget that WoW is based on the rich lore that exist, the story continues and evolves as it goes on, just like all other stories. The events in Wrath of the Lich King take place 4 years after those of the Frozen Throne and the merging of Arthas and Ner'Zhul (ingame there is 1 inconsistency with established lore though). But there is a lot of ranting and pretended herecy about Cataclysm.

Let's start with the new world out of the old world, lore wise... According to lore, Neltharion (or Deathwing as most will know him) was never killed, he merely kept hiding and manipulating after his defeat. He manipulated his only surviving consort Sintharia during the events of Night of the Dragon in Grim Batol. In short he has been plotting his grande reappearance for thousands of years. To remake the world in his image so he and his Black Dragonflight would rule all of Azeroth. So the world breaking up and burning all over is correct lore wise.

The flooding of Azeroth, lore wise... During the events of the War of the Ancients, queen Azshara and her arcane magic using Highborne Elves invited the Burning Legion with open arms to the world... of Warcraft. At the end of that First War, the Well of Eternity became ever unstable by the reckless use of its magic. Resulting in the destruction of Zin Azshari, the Night Elves capitol city and palace of the queen. The whole world became sundered (known as The Sundering) and ravaged and huge parts sank into the oceans. All that was left was an enormous vast sea with a never ending maelstrom where once the Well used to be. However as Zin Azshari together with the lovely queen and nearly all Highborne sank into the ravaging sea, she heard the wispers of the Old Gods. They promised her unsurpassed power if she would vow to serve them. She did... Azshara and the drowning Highborne did not die, they and their beloved city sank to the bottom of the sea and they became the Naga. Zin Azshari became Nazjatar (why call it Vashj'ir all of a sudden ?) from that point on. Enraged by the defiance of the Night Elves, the battle they waged on their queen and her defeat, she promised that one day the Naga would reclaim the surface world. So lore wise, the flooding makes perfect sense.

Arcane magic using Elves make also sense. Some of the Highborne felt it was wrong what the queen was doing, so they escaped Zin Azshari and joined the Night Elven army that fought the Legion. Some time after the War was over, the Highborne were exiled for being too arrogant and dangerous. Their leader Sunstrider (founder of the Sunstrider dynasty) renamed his Highborne the High Elves and left. Later ofcourse Kael'Thas took many of them with him and betrayed his people, they became Blood Elves. However some High Elves remained, Vereesa, Sylvanas and Alleria Windrunner amongst them. And since Tyrande is a big softy she would welcome the aid and return of their ancient cousins. Lore wise, arcane magic using Elves are correct. (My personal though on this is that maybe the High Elves should have became a separate race in the Alliance. The Alliance version of the Blood Elves. Just as arrogant and full of themselves. The High Elves differ a lot from the Night Elves in terms of beliefs, appearance, use of magic and their ideals).

The Dwarven Shaman, lore wise... During the events of Day of the Dragon, where Neltharion tried to manipulate his way to power within the Alliance and the Orcs had enslaved the Red Dragonflight and the Dragon Queen Alexstraza. The Dwarf shaman Falstad Wildhammer aided Vereesa Windrunner and Rhonin Draig'cyfail (or Dragonheart as some called him) on their mission to gather intel on what was going on in Grim Batol. Next to there clearly being a Dwarf shaman, the Dwarves have a history with stone and iron. Before the Old Gods bestowed the Curse of Flesh upon Azeroth (to prevent the Titans from destroying them), the Dwarves were beings of stone and iron. Lore wise it is correct that Dwarven shamans exsist.

The Goblins joining the Horde, lore wise... During the Second War, a Goblin Trade Prince agreed to ally himself and his faction with the Horde. The Horde was defeated during that time and so the Goblins decided to remain neutral, this would also benefit them more in terms of profits. Now with the Cataclysm caused by Neltharion (and probably Queen Azshara) the Goblins are in dire need of help. They choose the Horde because they already have a history of cooperation and the Alliance has an ally race which the Goblins don't like very much (probably the Gnomes). Many people already started ranting that now the neutral Goblin towns would become Horde towns. This will ofcourse not be the case, since these towns are run by the Steamwheedle Cartel under the rule of Trade Prince Steamwheedle. Who is still and will remain neutral and so will his towns. So Goblins joining the Horde is viable according to lore.

The Worgen joining the Alliance, lore wise... The Worgen originally come from another dimension or different plane of existence. Archmage Arugal has experimented with them and created Worgen/Human hybrids (Shadowfang Keep and Pyrewood Village). However their "lycanthropy" spreads and infected others. In this case it has spread to the secluded Human kingdom of Gilneas. Gilneas was a part of the (Human) Alliance, but their ruler Genn Greymane withdrew his support from the Alliance under the belief that his kingdom should not have to spend their resources on keeping their enemies, the Orcs, happy and alive in the internment camps. The great wall that separates Gilneas from the rest of the world was erected because Gilneas did not want to have anything to do with the problems of others anymore. In their isolation they are an easy prey for the Worgen and thus Gilneas has become infected with the curse of Arugal and turned them into the Worgen. Seeing as the Gilneans don't like the Orcs or Horde at all and they were once part of the Alliance, it is very plausible that the Worgen belong to the Alliance.

Dwarven mages and Gnome priests, lore wise... uhm, dunno. Seems agreeable that with the events in Cataclysm some "religiouns" allow others into their circle and allow them the same teachings.

Human hunters and Undead hunters. Why Humans did not get hunters from the beginning is a mystery to me. Afterall, what is so strange about a Human being a huntard... sorry hunter. The Undead being hunters as well then seems natural in my opinion. Why the Undead have no paladins seems also quite obvious to me. Lore wise... The Undead were all Scourge at first, but some broke free of the Lich King's hold and became the Forsaken. The filosophy of the Forsake does not at all embrace the belief in the Holy Light that the paladins believe in. The priests are in service to the Apothecarium. They bless and heal the Forsaken in battle and curse their enemies with pain, suffering and darkness just as they themselves once had to endure. The Forsaken are bend on infecting all humans with the Plague of Undeath and only allied themselves with the Horde because they could help them further their goals. They have no pitty, remorse or real feelings of friendship towards outsiders. They only want revenge on the living (humans) and Scourge for their suffering. The Forsaken are actually a 3rd faction in the game if you look at it closely. If any (playable) race in the game is truly evil and wicked, it is the Forsaken.

Tauren paladins and priests. According to lore, the Tauren were/are a nomadic and shamanistic race who worship the Earth Mother (probably the benevolent Therazane the Stonemother. A former Elemental Deity from the Old Gods). She is the creator of the world and all the beauty that nature holds. Her eyes are the sun (An'she) and moon (Mu'sha). In the occurring Cataclysm it is likely that some Tauren believe that they need more help from the Earth Mother and start to worship her other aspects (the sun for the paladins and the moon for the priests) to gain more ways to stop the destruction of her world. So them becoming paladins and priests is very plausible in the line of lore, although stretching it somewhat.

Blood Elven warriors. In their core, the Blood Elves are addicted to (arcane) magic and everything they do involves the use of it. The warriors may possibly be Blood Elves who overcame their addiction of magic. But a former High Elf who prefers a sword over a spell ? Again plausible but also stretching it.

Orc mages. In lore there are plenty of Orcs who use magic. Mostly it is the warlocks. But warlocks use fire magic and so do mages. Also in the Blackrock clans there are plenty of existing Orc mages, they were around ever since vanilla WoW. Orc society is based on shamanism and the warrior's way of life. Just like the presence of warlocks (despite the days of the corruption by the Legion and the Shadow Council), so too is it possible that the mages and their way of life from other clans like the Blackrock are now allowed.

Troll druids. The Darkspear and Shatterspear Trolls are part of the Horde, the Revantusk Trolls are allies to them. All the Troll tribes have always been very close to nature in all its elements. They have a heritage of war and blood lust and some still endone the practice of cannibalism and voodoo magic. It is possible that some have completely turned their backs to the old ways and completely embraced nature. So druids, who are one with nature, are not that strange in Troll culture.

So some things make good sense, others are stretching it. But most of them are logical results in a story that still goes on and adepts itself to the occuring events that simply were suppose to happen eventually to its own lore. The people who don't give a rats*ss about the lore and say the comming changes are retarded, well Blizzard is a company like all others and they need to keep the majority of their users happy in order to keep making money. But still, this is not the last WoW expansion. There still is the Emerald Dream/Nightmare and the corruption of the Green Dragonflight. Also the domain of the Burning Legion and the Nether itself where ultimately Sargeras will have to be dealt with. So, many changes and plot twists are still to come in the future of WoW.