This was really cool! The ghosts being invisible until you played your violin encouraged thorough exploration of the level, which was wonderfully varied and connected together in a very natural way. The soundtrack was haunting and paired well with the dark atmosphere of the environment!
In the standard build, I had trouble with the brightness–specifically, things seemed too dark, and some points were almost frustrating to navigate. The occasional lightning helped, but felt too sporadic to rely on as a means of illumination consistently.
Overall though, I think this was an excellent experience.