Its a Visual Novel. It was the first one I've ever played, and honestly did not know a thing about the gameplay of it, just the plot premise.
Its about a group of students who are all handpicked to join the school for Japan's elite. There you have people like the Ultimate Baseball Player, Ultimate Pop Star, and other teenagers who are the best at what they do. You play as Makoto the Ultimate Lucky Student. He is the average kid of the bunch who had his name drawn from a hat basically for the honor of going to this school.
Once they arrive they soon discover they are barred inside the school and have no way of escape. Monokuma (evil half white half black bear) tells them they either have to live out the rest of their lives inside the school or kill another student and avoid being found out.
People says it plays similar to Phoenix Wright games. You spend your time looking for clues, looking around the school or using free time to learn about your classmates. I completed my main play through in 21 hours, I'm still going for the Platinum at around 30ish hours or so.