Doolwind has written up an interesting post in his blog (which has been picked up by Gamasutra) about the limited nature of casual games (particularly those on Facebook), the lack of depth as a result, and therefore the high turn over rate that they are experiencing. People just aren't sticking to them because of the "very few operative and resultant actions" that the player can perform.
He cites Plants vs Zombies as a game that has very few operative actions but many resultant actions which creates depth and replayability, whereas a game like Treasure Isle has very few of both, leaving the game experience rather shallow...
(Doolwind) My hypothesis is that bringing the depth and emergence of a game like PvZ to Facebook would see more success than the current round of shallow games we’re seeing. A game like PvZ would obviously need to be changed to fit with the social nature of Facebook, but the key is that giving a deeper player experience, as well as the means for virality is going to see greater success.
For those who don't know Doolwind, he's a game developer who's since left the industry in 2007, however he's still developing indie games at his own start up in his off time. Read his entire blog post at the following link!
Great Article
The article is a great read. Very cool it was picked up by Gamasutra.
Doesn't apply to ALL Facebook games of course. Restaurant city is excellent. From a handful of pieces you can place you get some nice emergent behaviour from the diners. And I'm consistently amazed by the restaurant facades people are able to create with just a handful of themed pieces.