Kathryn Newton deserved better.
'Freaky' is largely a (very) mixed bag, but Newton's performance is honestly superb - which makes it difficult to rate. On the one hand you have a fairly run-of-the-mill slasher, yet on the other Newton's showing is of such quality that it belongs in something far greater. She's top notch here, it's just severely unfortunate the film is nowhere near her level at all.
There are a few decent slasher-y moments and Vince Vaughn tries. Speaking of Vaughn, it's neat to see a different side to him as an actor but I found him to be 50/50 in this; he kills it (pardon the pun) in some parts, but in others it's clear he's trying to impersonate a teenage girl - which is the complete opposite to Newton, who plays two characters supremely well.
I know I'm repeating myself, but... in layman's terms: Newton good, film bad.