It is impossible to understand if you weren't there how amazing these graphics were in 1985. We had never seen anything this beautiful on a ZX Spectrum screen. There was also a decent adventure game in there, but that was secondary.
The main distinguishing feature of the actual game was its attempt at grimdark realism, possibly inspired by the TV series, where you have to murder people left and right in order to proceed. This was another thing that we were not used to back in the day, but which has become all too common.
This actually scared me, something that can't be said of many horror games. The historical background adds a lot of depth, texture and terror. Despite the gruesome theme, it leaves most of the gory details to the imagination, and repetition and monotony are used to great effect.