This was the movie that got me buying a Blu-ray player, and I would say that despite the age of the source material, the quality of the print presented justifies hi-def. It is amazing the work that has been done providing a picture as good as would have been seen at the time in the cinema, a restoration perhaps triggered by the discovery overseas of a print of the movie enabling the damaged parts of the previous viewing print (from 1948) to be replaced. From parts of the original camera negative and two prints a wet gate print is made (by printing under a liquid with a similar refractive index to film base, the liquid fills scratches in the base, minimising their effect on the print) before applying modern digital restoration techniques to further enhance the image quality.
Something that surprised me (although with DVD and BluRay discs included it's academic) is that the BluRay had fewer extras than the DVD! Both have a featurette on the restoration of "UndergrounD" and the short "Under Night Streets", the DVD has another four shorts including the celebrated footage shot on the Metropolitan Railway in 1910, travelling out from Baker Street (I bet that gets a good few YouTube hits!) although it is the feature, with the emphasis on ordinary folk, that is of course the main attraction.
The language of the silent film is different to that of the "talkie" and sometimes requires much closer scrutiny of the image on the screen (seems obvious, I know - sorry about that) - but features such as UndergrounD provide a window into a world that is gone forever although we are privileged to glimpse shadows and hear echoes via contemporary films and recordings.
Coupled with which, of course, it's a cracking good story. and British....