Crowning Music of Awesome: The entire soundtrack. The top two being The Unfinished Swan, and the Monument Falls. Heck, a remix of the Monument Falls can be heard in Playstation All-Stars Battle Royale.
Nightmare Fuel: The third level, "Nighttime". Environment which is extremely dark? Check. Creepy sound design? Check. Giant spiders? Checkarooni. The first area in the game where you can actually be noticeably hurt by anything? CHECK.
It gets even worse in the PS4 version. The creatures that can hurt you hiss loudly through your controller's speaker when they attack. Have fun jumping right out of your skin the first few times it happens!