Joi Ito has a blog post on the key drivers of the bestselling game World of Warcraft (WoW). I believe the below insight isn't applied in many situations, including games (on any device), portals, websites or even a key presentation on a seminar. It resembles the ease of use and usability aspects of digital media in general but is slightly different. Fun is more attuned to our emotional level while usability is more functional. Both are important in my view. Fortunately, blog posts (like mine) are never more than 5 minutes ;-) BTW, the comments in the post from Ito are interesting to read as well as they show that even WoW isn't perfect alltogether.
"Although Rob - game designer of World of Warcraft (WoW) - was a hardcore player in Everquest, he designed WoW so that it allowed casual players to have as much fun as hardcore players. It really shows and as a guild custodian of a guild that has many casual players, the ability for casual players to have fun in WoW is very important. Rob mentioned that one of they keys to success of a game is to make sure that the game is fun in the first 5 minutes. I think many game developers forget this and focus on gamers who are "serious" and willing to invest significant time to learn to play or wait a long time to have their first "fun event". I think it is the breadth and diversity of the players that Rob tried to appeal to that is the key to success of WoW and he did it through attention to detail and trying to get each part right rather than focus on a single killer feature. It reminds me a bit of the book "From Good to Great" from Collins and Porras."