Within Rules of Play, the authors advocate something so phenomenal, I am compelled to quote it:
"We have a straightforward rule of thumb regarding prototyping and playtesting games: a game prototype should be created and playtested, at the absolute latest, 20 percent of the way into a project schedule."
My heart grew three sizes when I read those words. Look at the rule another way: At least 80% of a game's development cycle should be testing, redoing, and polishing. at least.
Imagine what awesome games could be made if design teams were expected to take 80% or more of their development time refining and perfecting their prototypes.
There exists at least one such game - Puzzle Quest. Infinite Interactive had a playable prototype for Puzzle Quest up and running after only 2 months. Then they spent an additional 25 months tinkering with, adding content to, and polishing the game. Having a working prototype just 7.4% of the way into their project schedule allowed them to develop a fun, successful game.*
While I couldn't find precise numbers for World of Warcraft, we can infer that a large part of Blizzard's development cycle is spent on iterative design, given the high level of value they place on game polish.**
In my experience, games like these are the exception.
I'll be keeping my eye out for other examples of games that followed the <20/>80 rule of thumb during development. It would be an interesting chart to look at game success vs. how much time dev teams spent in the prototyping and iterative design phases.
* The September 2007 issue of Game Developer has a comprehensive story on the development of Puzzle Quest.
** Rob Pardo's keynote speech for AGDC 2006 gives some hints on the amount of time Blizzard spends polishing.
I encourage all game designers to read Rules of Play, a game design textbook by Katie Salen and Eric Zimmerman.