Excellent effort which worked primarily because of absolutely superb choice & editing of music. It built suspense, tension and made us jump where we were meant to.
Reasonably well acted and dialog not overdone (the swearing didn't add anything so I'd suggest you replace that so as to be more "inclusive" in your potential audience)
But again I come back to the music. If proof were needed that sound accounts for 70% of the video and visuals only 30% this film is it. The dialog is actually superfluous as the pictures, foley and music tell it all. Keep the screams though
Where did the music come from and why wasn't it credited? I really hope you're going to say you or a colleague wrote it, or (even better so I can get it) it's from some sound library somewhere. If you've ripped it off (ie it's from a soundtrack album) I suspect if you showed this to budding composers you'd find someone keen to collaborate either on this or future projects.
Good luck and thanks for sharing.
Oh, and I meant to say, great opening title, too.