Reading it for the second time after its publication ended, I can say that it's still one of the best Psychological/gambling/death game manga out there. The author really put in an insane amount of research to bring out clever upsets, situations, and games. While reading it, I kept asking myself how large was the witheboard the mangaka's team used and how long they've been looking at it to make all the situations airtight. I cannot insist more: this is as clever as you'll find in any other manga, no contest. Yes, people mentioned that around the 2/3 of the story, the games unravel a bit, but it's not that bad. I'm personally mildly upset with how the 4th game (musical chairs) unfolds (I mean, from the start, why don't the non-players just follow the players, get their chair numbers, locations, and sell the info to other groups?! Or just move these chairs and hide them?). However, that game introduced a great antagonist as Harimoto who underlines perfectly the main character's strength (Yokoya and Akiyama are psychological strategists who win by manipulating the rules and people's greed, where Harimoto and Kanzaki use charisma, Nao being truly honest, and harimoto faking benevolence).
So people complaining about "the dumb monodimensional protag" either havent read more than 30 chapters, or have missed the character's progression entirely. Nao slowly learns from her mistakes game after game, and go from a hopeless rabbit in a viper's pit to an influence to be reckoned with in the later games.
Definitely recommend if you like complex psychological games.