Fred Topel reviewed Knock Knock for Bloody Disgusting and gave it 4/5 skulls. Here are some money quotes:
Evan is punished in a taboo thriller that will put Fifty Shades of Grey to shame. It reminded me of the glorious erotic thriller genre, but with a real edge that none of the ‘90s movies could touch, not even Basic Instinct. Knock Knock is dealing with a sexual manipulation deadlier than physical violence, but when it does turn violent, the tools of the violence have been so well established that it feels more brutal than Hostel.
Reeves is great with the kids, which adds to our disappointment when he violates his family’s trust, but also our sympathies when he gets in so deep. There’s also something special about watching one of cinema’s greatest action heroes (yeah, I said it) become the helpless victim.