Good watch, probably won't watch again, but can recommend if you've seen any other Parent Trap and not this one.

This holds up surprisingly well: Hayley Mills did an excellent job playing both of the girls. I questioned it once, but I honestly thought it was two different people during the movie.

That might explain why so much of the movie looked like green screen even though they established it was a real scene by interacting with it. It is also surprising how much 1961 green screen looks like modern 2020 "true motion" with a almost fake looking background.

Yes, it is quite a gimmick to do a "twins switch places", though that's partly because of this movie. It would be one thing if there were just a lot of twin actors looking to make it in the business, but today's climate would claim movies like this were stealing jobs from twins.

Though the movie is incredibly dated, it's actually interesting to see that 1950's motif where it was normal to have household staff still. The adults were a bit of a bore, it was the girl(s) fighting or getting along to antagonize the adults that really makes the movie, and that might be the big problem of it all. You have a young teen carrying the movie by doing double work, and the rest of the movie just doesn't feel loved. Sadly it shows the ethics of 1960's Disney.

The movie is fun though, and while I doubt anyone is going to watch it over and over again, it is definitely worth a watch, if for nothing else than seeing a birth of a trope.