After I showed Grumpy Goats to my game design students, we had a discussion about elements of Facebook games, and I showed them World of Secrets.
One might not think a Facebook hidden object game lends itself well to a co-op game for teenagers. (Have I mentioned my amazing gamer/teacher skills.) But we created house rules in which one player was on the computer, and the three others were circling found items on the whiteboard projection of the screen, so when the computer player got stuck, his friends had given him hints already! There was a great deal of screaming and laughing over finding the missing items, and a lot of excitement over completing the scenes.