The original and the remake essentially have the same plot. An unassuming family, John and Kathy Lutz and their three children, purchase a home in Long Island, New York that was previously the site of a mass murder one year earlier. While stating they don't believe in ghosts, the family has a priest attempt to bless the home, which is downright hypocritical. Families with wishy washy views on the supernatural always get targeted in these movies. Stick with your guns, everyone.
So, the priest becomes strangely ill and blind soon after the exorcism. In just four weeks, the family is forced out of the house following a series of haunted happenings. In the later version, Ryan Reynolds goes out in the rain in a t-shirt: this made watching the movie worth it for everyone's girlfriend.
George and Kathy Lutz (you see, they changed George's name to "John" in the movie to protect his anonymity) spent four weeks in the Amityville, New York, house in 1975, 13 months after Ronald DeFeo, Jr. murdered six people in the home.
You can see an interview with them here:
According to the couple, during their time in the house they heard voices throughout the day, there were various "cold spots" throughout the house, and they even witnessed green slime oozing from the walls.
Most experts and investigators who visited the house to study the paranormal claims dispute the authenticity of the story. The happenings are widely believed to be a hoax concocted for the best-selling book by Jay Anson.