The acting, needless to say, was very fine, and the plot and characterisation were faithful to the book but the script writing was quite flawed. Mainly, I think that the writer (or those who told him what to do) didn't trust the audience's intelligence enough. Look, we are a BBC 2 audience, we are sophisticated, we don't need things to be spelled out.
For instance, the gangster gives the hard-up aristocrat money. The next day a pretty seventeen year old boy turns up at Derek J's door with a contract. Jacobi lets the boy in, and signs the contract. The voice over says 'I hoped this didn't turn out to be a Faustian bargain'. Well, duh, we didn't need to hear that. The satanic figure, the helen-of-troy-boy, the contract. Even if you don't know Faust you kind of got it.
And this was the case throughout. You have one of the greatest living actors in the world, giving longing looks across a night club. You don't need a voice over that says 'I admired him'.
As a result I felt that the script didn't have enough space to build up the complex aura of menace that characterised the book. There was much to recommend it though, if they had only been a bit more courageous in letting the fine actors do their jobs.