I'm cautiously optimistic about this one. Depending on how it portrays the psychological gamesmanship (as well as the atmosphere of the games), this could be a fun ride. The fact that silence is integral to the rules of the first game makes the silence being broken at the end a stronger moment of contrast, which served as a good segue into the cliffhanger.
Manabu-kun definitely stands out. Since he acts as the group's ringleader (even though we've evidently seen higher-ups monitoring the games), he stands apart from them both design-wise with his nauseating colors and the animation used to portray him. A CGI person / creature against the supposedly-crisp, clean 2D friendship between the five friends.
If I do have any gripes, it's just that as is something that often happens with first episodes, it jumps into things rather quickly and therefore leaves the exposition a little more stumbling than it needs to be. That said though, I'm hoping that the rest of the material pans out!