As always, don't consider this advice to be a golden rule or silver bullet.

Separating fun and addictive can be really tough. I think many people show signs of addiction when playing their favorite games (which are probably the games they say are most fun). Just because you don't think Farmville is fun, doesn't mean it's not fun for someone else. Even if we assume that the tens of millions of Xbox owners all dislike Farmville, that's only a small subset of the hundreds of millions on Facebook.

Also, browser games can sometimes be less complex than a 3d AAA PS3/Xbox game that's built "from scratch". If users need to play it to "get it", you might be better off skipping the video and moving straight to creating a prototype that showcases the addictive features.