There's a huge factor in MMO success that goes largely unrecognised - the style in which the NPCs act.
I'm going to explain the two main different acting styles and then go on to give examples of how one style brings a MMO to life and the other makes it dull.
Let's start with a little history. In Shakespeare's time theatres were nothing like the polite and well-ordered places they are today. They were busier, they appealed to all members of the public, not just an intellectual minority, they were rowdy. Here's a short explanation.
To act effectively in that environment required eye-catching dramatic body language and booming voices with powerful projection.
Fast forward to the twentieth century and technology changed the ways in which actors could transmit story to audiences. Film and television focus completely on the actor with no distractions or background noise. Even theatres had become polite and quiet.
This led to the rise in popularity of method acting. Method acting is a naturalistic style that seeks to imitate the source. A method actor portraying a man digging a road wants to look exactly like a man digging a road. An old school actor would be trying to convey the feeling of digging roads: exaggerated shoves of the shovel, laboured sighs as he lifted a great load of earth, frequent mopping of the brow to convey the onerous and exhausting manual nature of his task.
Film and television critics have tended to support method acting. Old school acting techniques are called "hammy" and "overacted".
This has led to a bizarre blind spot in modern culture where many people believe that the best way to act is to accurately imitate rather than to entertain. Even when it's obvious that a commanding compelling majestic performance of emotional range is far more interesting to watch.
Spot the ham
Here are two cast photos. Both contain a member of the cast who is a veteran Shakespearean actor who uses old school techniques to add gravitas and emotional depth to somewhat trite sci fi plots.
Acting is where it's at, dumbass
Recent films like Avatar have stressed high tech effects over acting. For an example of just how unimportant effects are here's a clip from an old Doctor Who episode in which the Doctor and the Master confront an alien evil. See what they are battling so compellingly? It's a lava lamp.
You're drawn in by Jon Pertwee's tortured expressions and then Roger Delgado's convincing depiction of a man struggling across a room against great unseen forces. The programme doesn't need to show the forces, it just needs good actors.
The key to it is an actor who can project themselves so as to be interesting to watch. Many years ago long-running TV show Happy Days hired an actor to play a small role in one of its episodes. They got a man who was so fascinating to watch that audiences simply couldn't get enough of him and people are still fascinated by him whenever he appears.
On the set of 1976 film Marathon Man Dustin Hoffman was preparing for a scene in which he had to appear exhausted. Having stayed up all night he was setting off to run around the race track. Laurence Olivier asked him what he was doing. Hoffman replied I have to appear tired in my next scene. Olivier replied "Try acting."
What is old school acting and how is it done
Your goal is not to imitate it's to evoke. Exaggerated gestures, wild arm-waving, movement of the facial features, variance of the tone of voice are all elements. A person dying might fling their arms wide, scream, fall over, roll around. shout "I'm dying" and then slump dramatically. This isn't actually very like how people actually die, even when shot. You're conveying dying not mimicking it.
What's all this got to do with MMOs?
Simply that hammy acting works and method acting doesn't.
Warchief Thrall kneeling dramatically
Casilda, whore by night, method actor by day. So undemonstrative they had to physically tie her arms in place for this dramatic pose.
Ratongas - the Robin Williamses of EQ2.
Eve player - wooden.