Zero Series (Fatal Frame) is Japanese horror game. You fight against ghosts using camera. Speaking of Japanese horror game, those games which you fight against zombies and monsters such as Biohazard (Resident Evil), Silent Hill and SIREN. Different from them, in this game, a powerless girl explores abandoned building filled with ghosts by using "a camera which can take picture (exorcism) of ghosts".
Actually, I am a big fan of this game and have all these series. Especially, it is not too much to say that Fatal Frame II: Crimson Butterfly is the greatest horror game. Everything including story, character and the end of the story is beautiful and sad. There is no exhilaration to bring down zombies like in Biohazard. The appeal of this game is "silent fear" that a girl gets away from abandoned building alone in the midnight despite ghosts attack.
It took me three days to beat the game. I do not remember I could sleep properly. At night fall, I go to bed. The room becomes silent. If you play this game, you may think "A ghost stands on the corner of the room and stares me in the dark" or "If I close my eyes and when I open them gain, a ghost is laughing creepy near my face in the same way as in the game". Therefore, I don't recommend this game to whom having a problem with horrors. It is really scary!
It is scary but I want to play. I want to play but it is scary. I became hooked on this fear.
I recommend you to play in following order.
Fatal Frame II: Crimson Butterfly (2003)
→Fatal Frame (2001)
→Fatal Frame III: The Tormented (2005)
→Zero: Tsukihami no Kamen (2008)
Of course, it is good to play in original order. I wish this game is made into movie like Biohazard. I look forward to it for so long!