What's your favorite MMO feature?

Not all MMO are equally polished, fun or accessible. However even in the most criticized games there are great game play.

Among others here's a list of good mechanisms :

• 
  RIFT: class system. Being able to choose 3 talents trees and associated skills among 8 for each of the 4 classes. [Cons: won't likely ever be balanced by the devs... but by the players]
• 
  WoW: dual spec talent tree option [Cons: can create issues for sharing the loot. Too expansive for more casual gamers?]
• 
  SWG (pre-CU): lack of levels. Anybody is welcome to join any group. [Cons: can be confusing for the WoW generation of players]
• 
  SWG (CU, pre-CU): Skill trees instead of classes, and ability to respec into any template. [Cons: apart it was never balanced, can be felt a grind to go back once again through a former talent tree. ]
• 
  LotRo: fellowship maneuvers, making combat more more coordinated. [Cons: can be felt as complex to learn]
• 
  AoC: adding combos in combat. [Cons: not as convenient as a console combo system. Can be felt as password protected skills]
• 
  AoC: fatalities, the joy of beheading your enemy... [Cons: apart ESRB rating, bit too much random]
• 
  DDO: Character's collision and positional combat [Cons: you need to be coordinated to block a passageway. Creates lag in non instanced zones cf WAR.]
• 
  SWG: crafting from resources gathering to experimenting. [Cons: painful to manage the resource inventory. Click fest to grind. Not so easy at higher level]
• 
  TOR: crafting mini missions [Cons: none so far but that we don't know what's the real game play behind]
• 
  WoW taxy system, convenient to move around and get a drink while traveling [Cons: multiples hops can last way too long]
• 
  AoC and SWG: Character creation tool. [Cons: too often gear don't fit extreme body presets.]
• 
  SWG: in game access to the character creation tool (Image designer) to modify the character's body. [Cons: can be immersion breaking for some]
• 
  AoC: UI art, very clean and giving a distinctive look to the game [Cons: the UI features are one of the worst AAA MMO wide]
• 
  WoW: UI addons [Cons: in the end some mods become mandatory]
• 
  WAR: default UI features: show/hide/resize any of the UI element [Not as customizable as WoW with addons]
• 
  LotRo: Social clothing tab, don't need anymore to look like a twin or a mismatched walking clown [Cons:(for WoW devs) you are not obliged to display your high end gear at the AH]
• 
  GW2: 3 zones gear dyeing areas. [Cons: can end with weird choices, comes with RMT]
• 
  Aion: transferring stats from an item into another. [Cons: The noob pants you are equipped with might not be that bad...]
• 
  TOR: fully voiced over dialogs [Cons: not totally skippable. Can be an issue  for players not much into story]
• 
  SWG: Housing furnishing [Cons: Loads the game DB with thousands of items and heavy queries]

I'm certainly missing quite a few so what's yours?