The preparation to film the sequel began shortly after the premiere of the first film, but script problems delayed the project. Principal photography began in January 1935, with creative personnel from the original returning in front of and behind the camera. "Bride of Frankenstein" was released to critical and popular acclaim, although it encountered difficulties with some state and national censorship boards. Since its release the film's reputation has grown, and it is now frequently considered one of the greatest sequels ever made; many fans and critics consider it to be an improvement on the original, and it has been hailed as Whale's masterpiece. In 1998, it was selected by the Library of Congress for preservation in the United States National Film Registry, having been deemed "culturally, historically or aesthetically significant".