The casino also sells fancy penthouse apartments we can decorate more than other homes, slapping up pictures and slamming down sculptures. If you live in certain countries, mind, you'll be blocked from playing the casino games, presumably because of gambling laws. It's a social space along similar lines to the nightclubs, only dealing cards rather than pulling shapes.
The Diamond Casino & Resort opened in GTA Online today, bringing new cooperative story missions and new ways to gamble away your ill-gotten gains.