This version of the once banned Fanny Hill story clearly had a budget to burn: we have various familiar faces in the supporting roles. Most of them just show up to pay the rent, but Shelley Winters' portrayal of a madam is convincing. Also, a lot of money has been spent on sets and costumes. This alone makes it a lot more watchable than the average erotic B-movie, not to mention that the general light-heartedness in which the film approaches its subject is much more suitable for creating eroticism than the Erotic Thriller US style which so often combines sex with violence and death.
Still, this film has not managed to become a genre classic and it is not hard to see why. Most importantly, there is the actress playing the title heroine, Lisa Raines. While she's undeniably pretty (with or without clothes), her acting range is rather limited; it was probably impossible to get an established actress play such an exposed role. The 'innocent young girl' Lisa has to play at the beginning of the film is not completely believable, but much worse she completely fails to exude any sensuality in the later stages. This becomes especially obvious when we compare her to Maria Harper, the vampish actress playing the whore Phoebe. One gets the impression that Lisa/Fanny loves sex as a nice physical exercise in nice company. A similar criticism applies to her love interest: no charisma, no depth, and an instantly forgettable face.
This being a British film it doesn't come as a surprise that the sex scenes do not come across as very erotic, and that seems more of a cultural problem than a problem with censorship. The notable exception are the scenes involving the already mentioned Maria Harper. I suppose, there must be some Italians in her recent ancestry.