I think I know why it is relatively unknown. It was marketed as a cheap FPS (FPS were very big back then, as it was around the days of Doom. Everyone was churning out shooters of some description and the market share of such things was perceived as enormous) whereas it was an action/adventure in the vein of System Shock (albeit in a Gothic Horror way). As a result the shooter fans who bought RotH didn't get what they wanted and the action/adventure fans weren't aware that it existed. I actually e-mailed the Dev's about this as RotH was such a great game it made me sad to see it doing badly over such a mistake/misrepresentation, and they acknowledged I was probably on the right track in my analysis but it was out of their hands (publisher decision, as usual).