Kyle Orland, co-author of the forthcoming book Farmville for Dummies, writes this introduction to a two-part feature over at Gamasutra, by Tadhg Kelly. The title: "How Zynga's CityVille Has Compelled 70 Million Players."

Given today's surprising new interest in Cow Clicker over on Reddit, I thought I'd share some delightful snippets Orland extracted from Kelly's work.

One of the keys to this stratospheric player acquisition, Kelly argues, is the visibility and player base granted to the new game by cross-promotion through other successful Zynga games.

Once Zynga has attracted initial interest from its existing player base, Kelly says, the heavily click-based gameplay keeps those players engaged.

But the game's real addictive potential, Kelly says, comes from a never ending series of overlapping tasks that can never be fully completed.

Yeah.