The MMO community was thrown into a tizzy recently with the announcement that Undead Labs was open for business and working on a zombie-based MMO for consoles. Their website makes it clear that they REALLY love zombies. Even though vampires rule the roost right now, zombies are still pretty popular. Left for Dead 2 has sold over 2 million copies, and Zombieland made over 75 million at the box office.
There is a running joke among designers that every bad designer has an Angels vs Demons MMO design that they would make if they ran a studio. And that an Angels vs Demons MMO would be a terrible terrible idea. I know a couple of devs who would also add a zombie MMO to that list of bad ideas. I'm not sure I totally disagree. A zombie MMO is a fantastic premise, but you have to realize what the zombie genre is, and what it is not. And zombies come with a lot of problems.
In your traditional fantasy-based MMO, (and movie or book), the player starts out as a level-1 nobody and eventually becomes a bad-ass somebody. The experience is about the journey. It's about the evolution of the character into something heroic. You start out killing rats, and eventually, you find yourself taking down dragons. There is a definite thematic and systematic progression. It's essentially a retelling of the famous Hero's Journey story. People are very comfortable with the Hero's Journey. It shows up everywhere. It fits nicely into the three-act model and shares the same story "beats" that 99% of all movies share.
Zombies, on the other hand, are a completely different kettle of fish. While a zombie movie will follow the story "beats" that movie-watchers are familiar with, the "feel" is completely different. In a zombie movie, it's all about survival. The enemy is relentless and infinite. People can be heroic, but there is no "hero". The world is never saved. There is no power progression for the main characters - they either die or they don't. The formula for a good zombie movie is really powerful and should not (cannot) be messed with.
In a hero story, the hero conquers the main villain at the end and saves the world. In a zombie movie, usually either everyone dies or there are a couple of survivors, but their fate is uncertain. There is never a montage in a zombie movie showing the main characters becoming more skilled.
In a Hero's Journey-style story, there is a journey - duh! The hero goes somewhere and overcomes something. However, in most zombie movies, the main characters stay put. Their experience is about keeping the zombies "out". Exploration is only ever done out of absolute necessity. Usually, when the characters go exploring, they die. (Of course, the exception to this is the excellent Zombieland, which breaks all manner of zombie rules and regulations. In fact, I think there is an argument to be had that Zombieland isn't really a "zombie movie" - it's a road trip movie that just happens to have zombies in it.)
Now, zombie movies are awesome. They are easily my favorite horror subgenre. There is something terrifying and primal about them. I personally prefer the slow lumbering "inevitableness" of a Romero zombie to the sprinting relentlessness of an O'Bannon/Snyder zombie. If they can run, then there's no way you can get away, no way to be clever. You're just going to die. However, you can be clever and sneaky against Romero zombies.
Let's call what it feels like to be a character in a zombie movie, the "zombie experience". There are some features crucial to the zombie experience that are really problematic if you incorporate them into a DIKU-style MMO.
Guns are Weird. No-one blinks twice in WoW if you swing at point-blank range with a sword and get a MISS. However, it becomes aesthetically really weird if you shoot a shotgun at point-blank range and miss. That level of abstract nonsense becomes hard to grok. It's OK (but silly) to have to hit a monster with a battleaxe 20 times before it dies, but it feels wrong if you replace the battleaxe with a shotgun and get the same result.