2. Bingo
Bingo tends to produce considerable player loyalty and social interaction. Online bingo is as much a social activity as it is a gambling game. In the UK where bingo is most popular, chat windows and private game lounges have helped spawn hundreds of in-real-life friendships.
The repeat visitor nature of bingo games should be credited in part to the organizational structure of the game. Playing a bingo game requires an upfront time commitment that many people are not willing to invest. So there is a built-in filter with bingo where the people who play it are typically people who will be very interested in playing it again.