If your login screen looked like this the last time you played World of Warcraft, this article is for you. I've done my best to cover all major changes that are still relevant, beginning with Wrath of the Lich King. I didn't start playing WoW until Burning Crusade, so I couldn't explain how that expansion changed the game without ripping information from another site (and that would be cheating). Feel free to skip over any of the expansions below if you're already familiar with them.
Wrath of the Lich King
-New continent: Northrend - Venture to the frozen north to fight zombies, giant vikings, dragons, zombie dragons, and giant viking zombies riding dragons! Wrath was the latest expansion to feature 10 levels of questing content (increasing the cap from 70 to 80), and it is an absolute blast. The environments are breathtaking (unless you hate snow) and each zone has a coherent story that is advanced at an appropriate pace through questing. Oh, and the music is fantastic.
-New class: Death Knight - The first - and still the only - hero class. Death Knights are the only class to have a unique starting experience, and new Death Knights start at level 55. As such, a player is required to have at least one character at or above level 55 before creating a Death Knight. The Death Knight is plate-wearing melee fighter with some casting ability - similar to a Paladin, but with the ability to raise undead minions. Death Knights make exceptional tanks and damage dealers.
-New profession: Inscription - Practitioners of Inscription ("scribes") mill herbs into ink to create scrolls, enchanting vellums and glyphs. Which brings us to another, very important new feature...
-Glyphs - A new way to customize your character, glyphs currently come in two varieties - major and minor, limited to three each. Major glyphs function similarly to talents, and generally beef up existing spells and abilities. Minor glyphs are cosmetic, or add non-essential functions to existing abilities (such as causing Polymorph to last for 24 hours when cast on critters).
-Heirloom items - Heirlooms are a new type of item which are account-bound. High-level characters can purchase heirloom items, which scale with level and usually provide an experience boost, and mail them to lower level characters on the same account. Heirlooms are the only items which can be mailed cross-server and cross-faction.
-Dungeon Finder - Dungeon Finder was a game changer for casual players at the level cap. By opening up a very friendly interface (by default, bound to the "i" key), players can queue up - solo or as a party - for a random or specific level-appropriate dungeon. Dungeon Finder made queuing for random low-level dungeons the quickest way to level up, and running random max-level dungeons the easiest way to obtain gear for new level 80's.
-Achievements - Achievements in World of Warcraft are more-or-less the same as achievements on Xbox or trophies on PlayStation. Finally, a way to quantify how awesome you are as a player.
-Pet/Mount tab - Pets and mounts no longer take up bag space, and have been moved to a new "pet panel", bound to shift+"p" by default.
-Multiple raid sizes - Every raid introduced from Wrath on has featured both a 10-man mode and a 25-man mode, causing a divide in the raiding community between 10-man guilds and 25-man guilds. Later in the expansion, heroic modes were added to both sizes.
-Dual talent specialization - Now, players can learn the ability "Dual Talent Specialization" from a class trainer for the ability to have, you guessed it, two sets of talents and glyphs. Dual talent specialization allows players of hybrid classes to have, for example, one healing spec and one DPS spec. Pure DPS classes could opt to have one PvE spec and one PvP spec. Switching specializations incurs a modest cast time and drains all resources, and cannot be done while in combat.
Cataclysm
-New questing zones in Kalimdor and Eastern Kingdoms - Cataclysm was unique in not adding a new planet or continent, instead focusing on changes to Kalimdor and Eastern Kingdoms. The new leveling zones are scattered across Azeroth, but breadcrumb quests in the faction capitals (Stormwind and Orgrimmar) make travel easy. Cataclysm was also unique in adding only 5 levels of content rather than 10. The new zones are entertaining, and introduce some new, gimmicky quest mechaincs (like throwing baby bears onto a trampoline, or using quick time events to wrangle a giant seahorse). The new zones feel novel and interesting, but don't contribute to a coherent story-line.
-Revamped 1-60 questing experience - Cataclysm's lack of endgame focus is fully compensated for by its total overhaul of the 1-60 experience. New, more engaging starting experiences have been designed for all races except Blood Elves and Draenei, and every zone in Kalimdor and Eastern Kingdoms has received similar treatment. Quests are less scattered and overall more fun.
-New races: Worgen (Alliance) and Goblins (Horde) - The Alliance got a brand-new race of werewolves (complete with the ability to shift forms anytime out-of-combat), while the Horde got the previously neutral race of Goblins. While some felt the Horde was getting the short end of the deal, Goblins ended up having a totally awesome starting experience and a few choice racial abilities.
-New profession: Archaeology - Archaeology is a secondary profession, so there is no need to replace a profession to learn it. Archaeology involves visiting randomized dig sites across Azeroth (and Outland) to find fragments of artifacts. Once enough fragments are retrieved, they can be combined to create restored artifacts, which can include fun toys, powerful weapons, vanity pets and mounts.
-New race-class combinations - Tauren Paladins! Dwarf Shamans! Troll Druids (oh my)! Blizzard lifted some race-class restrictions in Cataclysm, allowing combinations that, lore-wise, would previously not have made sense.
-Guild advancement - Blizzard gave characters a new incentive to join and participate in guilds with a Guild advancement system. Guilds now level up and award perks to members. These perks include an experience bonus, a massive AoE resurrection spell, and a shorter hearthstone cooldown.
-Flying on Azeroth - The cataclysm also apparently broke the mechanism that prevented players from flying in Kalimdor and Eastern Kingdoms. Level 60 characters can now purchase a "Flight Master's License" to fly in the old world.
-Transmogrification - Transmogrification was patched into Cataclysm fairly late in the expansion's life. It allows a character to change the appearance of an equipped weapon or piece of armor to that of virtually any item the character owns. Void storage, a new bank-like feature, was introduced specifically for storing transmogrification items. Clownsuits are now optional.
-Raid Finder - Functions the same way as the Dungeon Finder, but for max-level raids. Raid Finder assembles 25 players into a balanced group, and features an adjusted difficulty which is more forgiving for players who cannot coordinate as well as a premade group. Raid Finder gear is better than Heroic Dungeon gear, but not as good as Normal mode raid gear, and serves as a bridge into normal raiding.
-Rated battlegrounds - Just like arenas, battlegrounds now include a rated mode. Arenas and rated battlegrounds award conquest points, which are used to purchase top-tier PvP gear. Unlike regular battlegrounds, players are unable to solo-queue for a rated battleground, and must form a premade group. Currently, only 10v10 battlegrounds are available as rated battlegrounds.
-Darkmoon Island - The Darkmoon Fair, a montly in-game holiday, now exists on its own mysterious island. Darkmoon Island opens for one week beginning on the first Sunday of each month, and contains minigames which award Darkmoon Tickets (which can be used to purchase prizes) and repeatable quests which raise skill in any profession.
-Beautiful water - Water, which had always existed as a tiled, animated image, has been updated! Water now splashes and ripples when disturbed (even by the rain), and properly reflects light.
Mists of Pandaria
-New continent: Pandaria - Believe it or not, the expansion that introduced kung-fu practicing, ale-brewing, comically rotund panda people has a moving story which is both deeply political and surprisingly dark. The conflict between the Alliance and Horde leads to the accidental discovery of Pandaria - a pristine continent which has known peace and prosperity for thousands of years. The Horde and Alliance each begin a campaign to conquer Pandaria and enlist the natives in the war effort. In the turmoil, an ancient force which feeds on negative emotion awakens and threatens to destroy Pandaria. This expansion holds a mirror up to each faction, and forces the player to consider the implications of his/her actions. This expansion, like Cataclysm, includes 5 levels of content and features some of the prettiest scenery ever to grace the World of Warcraft.
-New race: Pandaren (Alliance and Horde) - Pandaren players begin factionless, as martial arts students living on the back of a giant turtle. When the Horde and Alliance arrive, players must choose a side in the conflict.
-New class: Monk - Monks are the third true hybrid class, with specializations for healing, tanking and damage dealing. Monks are leather-wearers who fight hand-to-hand, drawing their weapons only for specific attacks. Each specialization has access to melee attacks and spells, which may use mana, energy, or a unique resource called "chi".
-Talent overhaul - Talents no longer exist as spec-specific trees, and have been redesigned from the ground up. Players now choose one class-specific talent (of three) every fifteenth level. Unlike before, each talent selection adds a new ability or significantly alters an existing one. There are no "cookie cutter" builds anymore, and virtually every talent is viable for every spec and role.
-AoE looting - A HUGE quality of life improvement - right-clicking to open up the loot window on one enemy now shows loot for all nearby enemies. This means that for large AoE pulls, a player needs to loot only one corpse.
-Pet battles - Most vanity pets can now participate in 3-on-3 pet battles against other players and wild pets. Each pet belongs to one of ten families, and each family has a passive ability and relative strengths and weaknesses which should look familiar to anyone who has played Pokemon. Pets may have three abilities at a time, with a total of six being learned through leveling up (to the current level cap of 25). Wild pets can be captured and come in four qualities (poor to rare) and multiple breeds with different stat distributions.
-Scenarios - Scenarios are best described as short, story-driven dungeons. Like dungeons, players can queue for random or specific scenarios which are classified as either normal or heroic. Unlike dungeons, scenarios require only 3 players (with no specific roles), and have no traditional bosses. Players receive loot from scenarios in the form of a "Cache of Treasures", which is awarded after completing a scenario and has a chance to include gear which is comparable with dungeon loot.
-Flexible Raiding - Raiding now comes in another size... sort of. Flexible raids may have between 10 and 25 players, and will adjust in difficulty based on the number of players present. This means that 10-man guilds never have to bench members and 25-man guilds can run without all members present. Flexible is ranked between Raid Finder and normal mode raiding. In the future, 10 and 25-man normal and heroic mode raiding will be replaced with normal and heroic flexible raiding.
-Brawler's Guild - Blizzard has described the Brawler's Guild as solo PvP, which is fairly accurate. After obtaining an invitation to the Brawler's Guild, players may challenge NPC's to combat. The mechanics of each fight are complex, and a time limit is imposed. The Brawler's guild rewards only vanity items - titles, mounts, and the like.
-Proving Grounds - Proving Grounds provide a safe environment for players to master a role - tanking, healing or damage. In tanking or healing mode, players are tasked with aiding a party fo NPC's in clearing waves of enemies. In damage mode, players have no party, but are not actively attacked by NPC's. Each role has four ranks - Bronze, Silver, Gold and Endless. In the future, a silver medal in Proving Grounds will be required to queue for heroic dungeons.
-Challenge mode dungeons - In challenge mode dungeons, all gear is scaled down to ilvl 463 (the same level as loot from heroic dungeons) and completion is timed. Completing a dungeon within a specified time limit will award the player a Bronze, Silver or Gold medal in that particular dungeon. Rewards from completing challenge mode dungeons include titles, mounts and statless armor for transmogrification.
