First, it's a feast for the eyes. Gorgeous sets and magnificent period costumes are highlighted by cinematography with an eye toward the poetic and artistic. Every scene is composed with great care and detail. Flawless.
Second, it has an intelligent and creative script that puts a new spin on the Jack the Ripper legend. This time, it's his daughter who is doing the killing after she witnessed her mother's murder at the hand of her father (Jack the Ripper) when she was a child. Now she's 16 an finds herself blacking out for periods of time, not knowing exactly what is happening. Fortunately, a compassionate (and a little obsessive) psychologist takes her under his wing and is determined to find out what's going on with her, suspecting the worst.
Third, the acting is impeccable and while the "English whores" are a bit of a caricature, the rest of the cast is delightful to watch. Dr. Pritchard is played by veteran Shakespearean actor Eric Porter [The Lost Continent, Day of the Jackal] who bears an odd resemblance to Kevin Spacey. He appears in almost every scene in this film and brings a wonderful depth to his character. Angharad Rees [Poldark, Jane Eyre] is also great as Jack the Ripper's daughter. She never overacts and gives a subtle but powerful performance, capturing both the emotions of innocence and malice with great skill.
Do not miss this one. It's definitely an overlooked gem from the wonderful body of work created by Hammer Studios.
For more info check out the film's entry in IMDB.