Attention:
Don't watch this when you're eating.
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.