My feelings went Beginning: Excited Because I had no idea who the serial killer is. No information.
Middle: Suspicious Because I made a different scenario in my mind that it was actually not happening. He's a sociopath so he made a scenario in his mind and it wasn't happening at all. Or the serial killer was him.
Ending: Disappointed Don't finish like that. Totally went a wrong far away from what I thought and that wasn't nice for me because you must check it out yourself. However horror movies lovers may like the ending.