It's not trashy, unlike the 2017 anime. It's comparatively subtle and eerie, in fact. It's fairly good. However it's also another low-budget J-horror that's trying to make a virtue out of its cheapness, while being understated in a way that might seem dull compared with the lurid, sleazy anime. (In fairness, of course, that anime didn't exist in 2011.)
The plot's the same, except that the film's sensibly adapting only one King's Game instead of two. Every day, everyone in your high school class gets a text message from the King. You must obey. If you don't, you'll be punished. At first, these orders are relatively understated and might even be called benevolent. They're pushing people in new directions that they hadn't had the courage or imagination to do for themselves. "Confess your love to the girl you like." "A and B must kiss." (A doesn't mind at all and indeed gets flirtatious about it, even though B's impersonating a block of wood.)
That doesn't last long, though. Things escalate. People reject their orders and learn what the King's punishment means. (Unlike the anime, you simply get "erased". This doesn't involve gory suicide, although there's no guarantee that someone won't do that pre-emptively to avoid erasure. In short, you disappear from the world. You unhappen. Your family and teachers forget that you ever existed. Your school desk fades away.)
This feels like a fairly cold, distant movie. People keep disappearing, until eventually the classroom's almost bare of desks and yet the teacher will still trot in saying "no absences again today". The King's orders turn classmates against each other. There doesn't seem to be any way of resisting, since the King has magic powers (omniscience, reality-rewriting, etc.), so it looks as if everyone's doomed and we're just watching a not-very-friendly class of high school students fail to hold together in the face of extreme Darwinism.
I think that coldness, though, also comes from the movie's cheapness. It's not visibly cheap, mind you. It's perfectly watchable. It doesn't look amateurish or anything. However it's doing that Roger Corman thing of "let's shoot this as quickly as possible" (albeit with a very different tone), by regularly shooting in a single long shot with no close-ups and using pans rather than cuts. This keeps the cast surprisingly far from the camera. Important character beats might well happen at a distance... but unfortunately this might be for the best, since the cast includes several idol group members. Jealous Boyfriend can't act, to a degree that's visible even from the other side of the room. There's one of the weakest "just about to kiss" moments I can remember in anything. This is a cast that almost mandates this shooting style, although in fairness most of the acting here manages to be sort of okay. No one's good, but most people manage to deliver their lines without tripping over or anything.
Scenes usually happen in the classroom, even when they don't obviously belong there. A shy boy has to ask out a girl, or else a girl has to kiss a boy. I was surprised that they did that in front of everyone, although in fairness that's more attention-grabbing. The film's understated nature will also have helped the budget. Quiet things happen quietly. People don't die in gory, flamboyant set-pieces. You can do a simple disappearance with a cut... and in fact I thought the film would have been better had it taken this even further by removing its one use of spooky disappearing CGI.
The plot's simple, but the logic behind it is complicated. The King's Game can be whimsical with its rules, usually but not always giving you until midnight to obey. One girl gets about thirty seconds. She runs out of the room and that's it. Bye bye. That was a bit extreme. There's a nice bit of logic involving the photos, which the film then muddies by having some logic at the finale depend on a near-identical photo-based assumption. I'll be generous and assume that was deliberate. We're wondering if someone's about to be murdered based on invalid logic. However the reason for the King's Game is far less absurd than the anime's. I don't imagine it made sense to everyone, but it seemed pretty reasonable to me if you think about the King's Game's blind idiot logic and magical powers.
On the downside, everyone who receives a text message will always read it aloud.
It's a simple film, in a good way. The popularity poll, for instance, was almost startlingly down-to-earth compared with what I'd been expecting from the anime. It's not sleazy, despite a scene where someone tells Chiemi to undress in front of the whole class. The film won't have cost much to make, but in practice that comes across mostly as realism and understatement. Some shots even look almost stylish. That said, though, it's not really aiming for "scary" and we're not really being invited to embrace the characterisation, so I'm not convinced you'd ever feel the need to rewatch this film. I thought it was okay. It would have seemed more startling if I hadn't just seen the anime, but if so then I'd have probably never hunted it down in the first place. It's a reasonably good J-horror, but also a bit drab and you might find it slightly dull. It works, though. I think it succeeds at being what it is.