CONTAINS MODERATE SPOILERS AND BOREDOM
It's our own fault. Because we die-hard horror fans are apparently so forgiving of movies that aren't terribly good, the genre is swamped with movies made to a lower set of standards. You wouldn't get away with a courtroom thriller that was full of plotholes, or an emotional drama with performances of the "reading aloud" variety, or a romantic comedy where there was not a whit of chemistry between the participants. You wouldn't put out a chase movie where the cars don't go above 25 mph. But people - and that's us - will seemingly accept a slasher movie that's inadequate on all fronts: logic, suspense, and plausibility (not to mention the inadequancies in acting, writing, editing, scoring, photography etc), so long as it delivers on the gore and, as a lesser priority, the sex.
A case in point is Knock Knock, a dreary plod through the campus slasher handbook without any interesting riffs on the themes of the genre, without any notable additions to (or deviations from) the themes of the genre, and indeed without more than the most rudimentary filmmaking skills. We're squarely in I Know What You Did.... territory here, as comely teens and halfwitted jocks are being violently slaughtered by a masked psychopath as revenge for past misdeeds - a dark secret that nobody even mentions for the first half of the movie but maybe it's got something to so with the football team and the handicapped janitor. Acting, even by genre standards, is first read-through standard at best, you wouldn't believe the female lead if she told you it was Thursday and you certainly don't believe she's a detective. Maybe a poledancer or a rollerblading waitress, but not a detective. The cinematography (more accurately videography?) gets the shakes every time the killer gets down to business, though that may be an attempt to disguise the ropey nature of the splatter effects. Meanwhile, one significant character is introduced early on in the movie and then disappears for more than an hour.
Yes, it has plenty of gore in it, although it's not particularly impressive, and it has plenty of college cuties willing to parade around in minimal shorts and skirts, or indeed nothing at all. One early sequence features a female student thrusting her frankly grotesquely massive chest in the face of a dimwit jock - a scene of no importance whatsoever as it's the only scene she's in. But hey, get a load of those whoppers, lads! Frankly, if all you want is boobs and bums, rent a porn film and be done with it. Knock Knock, meanwhile, is exceptionally shoddy and completely and utterly not recommended. Not even a little bit. We deserve better.