Pick up the sound track and you will love it. I listen to it all the time and the inclusion of the Van Morrison hit "into the mystic" sets the mood for any situation. Beautiful movie and all time classic.
Several improvements are made on the classic "Freaky Friday" theme. For thing, Feldman and Robards are adversaries. For another, it is not just Robards and Feldman that make the switch. His wife has too but she doesn't realize it. She, as Feldman's young girlfriend, doesn't understand why she can't remember her locker combination or dance routines. As Robards, with help from Haim's character, tries to adjust to life as a high schooler in the days of mousse and Michael Jackson, he is haunted by cryptic dreams where Feldman - who seems to know more than he is letting on - warns him that he must make her realize who she is before it is too late and Robard's wife is lost forever.