Definitely one of the most well written and mystical FM.
I always find music/ambient the most important component in FM and for genres like horror its especially important. Undulating terrain by Robert Rich fits absolutely perfectl here. It feels like it will be the endless night and the sun never rose in this place.
Another thing I like about this FM is that there is no screamers, everything built on the atmposhere.
SPOILER:



And another interesting detail that we emphasize at the end of the mission is that there is no one in the castle except us, we do not know this during the game and carefully listen to the sounds.

If you like the fm then you shouldn't include such immersion breaking gameplay spoilers for those that haven't played it.

EDIT: Saw that you edited the review, sweet! Now there's no problem.