I enjoyed the room with books named after the author's other fan missions, and the gramophone and readables, although the latter were immersion breaking for Thief. The carrot easter egg was neat too but also immersion breaking.
Over all, I played this mission right after the author's Invitation to Castle Morgoth FM, and right off the bat there was a reduction in the immersion experienced in that mission. The nice thing about this mission was the relatively solid mansion job, and a nice three page map of the building. Unfortunately I had to backtrack and scour through the entire mansion to find a certain coin after I had finished everything else, and still had no idea to go and had to resort to looking up the answer online. That puzzle wasn't very obvious which made the mission hard to complete.