I would like to preface this review by saying that I haven't finished this manga, nor do I ever intend to, but after looking at other people's reviews I doubt that the ending would change my opinion of the story at all.
The story for Ousama Game is simplistic, which isn't necessarily bad but doesn't help it much. A whole class of students begins to get texts from someone named "Ousama" that tells them to do things, but the tasks quickly escalate from juvenile things such as kissing and licking another's foot (for some reason...) to telling other students to die. This could be an interesting study of group psychology, but it's handled poorly. One point that I noticed immediately was the lack of any intervention from authorities. Other series with similar plots explain this by either having it set in an isolated area where no one could possibly help or have it so getting authorities involved would be in direct detriment to the contestants to the game. These situations don't apply to Ousama Game, and as the series progresses it only becomes more silly that police nor the school administration haven't taken action. I know that Japanese school systems don't like to touch the matters of suicide, but when multiple students in a class have all died in a short period of time, with almost all of them being "suicide", you'd think that someone would say "Hey, wait a minute, something's not right here.". Later on, some students say that they've tried telling the police and have gotten no response, but at this point it just seems unrealistic and contrieved, which totally broke my immersion in the story. Also, as the story continues past the initial mystery, more and more plot holes open up and make everything confusing to the point of it being unenjoyable.
I enjoyed the art style, and there weren't many glaring flaws in the art. However, it isn't really special. Not much to say.
I have never experienced such an unlikeable cast of characters that do not seem to serve any other purpose than to push the plot forwards, even if it seems wholely irrational. Part of this is intentional, because a murder game like this would understandedly stress people out and cause them to act weirdly, but there comes a point where it passes realistic stress and falls into the pit of absurdity. The only character that I came remotely close to liking was Daisuke, and that's probably only because he died before he could become annoying.
Don't get me wrong, I wholly dislike this manga. However, reading it is such a wild ride of things that make no sense that it's almost a comedy. I may not have enjoyed it for the reasons the author intended, but goddamn some of this was unintentionally funny. If you want something to read with friends on a call, this is absolutely it.
I'm sure others could find this enjoyable unironically, but I didn't. I wouldn't recommend it unless you either are willing to look past major plotholes or are looking for something that's so bad it's looped right around to being a fucking comedic masterpiece to read with friends.