Waste of time *big spoilers*
Stupid, unbelievable plot; tons of stupid character decisions, most of them from "seasoned" police officers; Skills of the antagonist clearly exaggerated, story fitted so she gets the upper hand every time, her transformation into such a psycho after the loss of her child is also unbelievable. I mean, why the hell would she kill the cat?? lol
She doesnt only want the child in the movie, she wants to get in the messiest and most macabre way possible, all of course to shock the viewers.
Regarding the stupid character decisions:
Cops:
1. cop #2 goes rather upstairs for sightseeing than to help his colleague arrest the perpetrator who has slaughtered at least 2 people already (from his pov)
2. cop #2 is yelling at the protagonist to open the bathroom door with his back turned to the stairs. I mean, cant you yell while covering them?
And I mean, even cops in civilian clothes should have a radio to call for backup huh? But no, we must give the femme fatale a fighting chance, so she can finish them all off 1 by 1.
3. cop#3 taking a civilian into a slaughter house and chaining him to himself impairing his own combat capabilities.
4. cop#4 assuming that the villain has left the house just by checking a couple rooms and seeing an open bedroom window and then putting the victim into that very same bedroom, i mean come on!
5. Cop#3 not taking the victim with him and leaving the house. He feels compelled to leave her alone in no fit state to defend herself. Being a gentleman though, he gives her a gun (which she, most conveniently for the writers, abandons after being attacked by the femme fatale, which by now seems to have the stealth of a highly skilled assassin).
Ah yes, another "small" plothole. The deranged antagonist who managed to kill 6 people couldnt break open a bathroom door while having all the appliances of a household at hand. No, she would rather sit in front of it and kill the cat out of boredom while waiting for it to magically open itself
Conclusion: Dumb plot, dumb characters, lots and lots of gore - only thing this movie has to offer.