The PE series are a unique breed of horror games – they mix the typical gameplay elements of survival horror(cinematic camera angles, item finding, puzzles) and RPG(experience gathering through fighting, levelling up etc.). There is absolutely no other game series, or any game for that matter, mixing those supposedly unmixible genres, AND doing this surprisingly well all at the same time. For that alone they are worth checking out.
Storywise the games are fan-fiction sequels...