Complex sentence: The original film was an adaptation of "Carmilla" by Joseph Sheridan Le Fanu, however "Lust for a Vampire" shared little with the novel and only used the vampire characters, and was thus a completely new story.
Split into simpler sentences: The original film was an adaptation of "Carmilla" by Joseph Sheridan Le Fanu. However, "Lust for a Vampire" shared little with the novel; it only used the vampire characters, and was thus a completely new story.