The game or the movie?
The game is fun. You are a security guard holed up in an office in a Chucky Cheeses (Fazbear Pizza) where demonic possessed animatronics wander at night and slowly make their way to your office to do terrible things to your body. Basically you have to survive the night until 6am. You have a limited range of options to monitor and protect yourself from the animatronics. You have your trusty security monitors to monitor their whereabouts, light switches at either door exiting your office which light up the hallway (hallways are pitch black on either side, so unable to see animatronics till you turn the lights on, which flicker). You also have security doors on either side of your office. Turning lights on and shutting doors (even using the cameras) all consume battery power so you have to be wise and use them sparingly as you won't last the night just leaving your doors down or spamming the lights too often. Once the battery goes out, you are pretty much fucked, Freddy will come out and jump scare you. As more nights pass, the animatronics get more bold and aggressive as they make their way to the office which makes battery management a real killer when you have animatronics showing up at both sides of your office at once.
Each mobile FNAF game and its sequel is kind of a variation of this formula.
The movie:
Well, I wouldn't really say it was scary but lots of nice lore drops. I doubt the movie will be popular for people not familiar with FNAF, but people who played the games or are a fan should appreciate it. I thought the movie was worth seeing at least once, as a person who enjoyed the games.