I've always heard of this, and its later remake, but never got around to watching it. I have now and I thoroughly enjoyed it. Hayley Mills, just like in 'Pollyanna', is infectious so you can't help but like her character(s). She does a respectable job playing two parts here, the camera work and editing in that regard is exceptionally good - I didn't notice any major issues with the special effects or body double(s). Brian Keith and Maureen O'Hara portray the parents of Mills' Sharon/Susan, both adding positive elements with their performances. I like the dynamic between the two, even if their characters aren't perfect; especially with the sprinkling of domestic violence from O'Hara's Maggie. The plot, which I had heard about beforehand, is certainly interesting. They do a fine job at melding it together and making it feel more plausible than it is. With that said, I do believe the run time could've been shorter as the third act is a little uneven in my opinion. A fun film, mostly thanks to the delightful Hayley Mills.