The idea of a Death Game isn't exactly new, but I usually always enjoy them. So I did like this drama too, but I didn't love it. The writing had quite a few holes, but it didn't really bother me because I wasn't super invested and just didn't really feel the tension. It wasn't that the stakes weren't high--they were, but I think because the characters weren't developed like they should've been, I didn't care about anyone too strongly. Even Yoonseo, who's supposed to be the lead, hardly felt developed.
I also guessed they were really in a game a few episodes in (or it was all dream) just because of the way the kids lost control and killed themselves and because of the moment everyone suddenly remembered the girl who'd died in the real world. Also when Junhee suddenly came back to life. That was a pretty clear sign this wasn't real life.
But like I said, none of that really bothered me and I enjoyed the drama for what it was.