It's an interesting game for sure. As in, the concept, since the gameplay is only set dressing for whatever the creators had in mind. The fact that all the signs to figure out whether or not someone is a Visitor are so vague and common and that there is an entire mechanic where you have to counteract those signs as they happen to you to not get considered as one, like smoking cigarettes to yellow your teeth, just adds to the paranoia fuel the game's premise is based on.
As for the game being vague as shit, I think I know where the people behind it got their inspiration from.
For context, back in 2013 when the first episode of Smile Guide dropped, no one had any idea who was behind it or what it was. It was a complete mystery and nothing in the videos was pointing to anything concrete, so people were trying to make sense of it, connecting all the clues scattered in the videos to come up with an explanation but everyone had a different interpretation. However, the most common theory was that it was about a global nuclear war, due to the series having a ton of hints like Cold War PSA's spliced in-between or the corners in every series being analogous to the INES scale.
Only after the project was finished and the creator revealed his identity, years after the project began, he explained that his intention was to make it so vague so that people would come up with their own interpretations. Something that all the analog horror clout chasers won't ever get and will forever make hot garbage as they demand immediate asspats instead of trying to actually make something interesting for people to enjoy.
I feel like that's what the devs were going for. Leave enough ambiguity for people to come up with their own theories. Why is the sun acting up? Have we destroyed Earth's natural protection layers so now sun's activity is this disastrous? Is it still intact and it's the sun flaring up? Why is it flaring up? What exactly were the Visitors? Have they returned back where they came from? Are they still around? What does the world look like after the events of the game? What exactly is FEMA and what they're doing? All intentionally left open-ended for people to make up their own stories, but since we live in an era where every horror story has to be meticulously explained to the very last detail the idea falls on deaf ears.
