I saw the 2007 French/American version of this film first without knowing it was a remake. I liked it, especially the performance by Olivia Thirlby, but when I discovered the 1999 Japanese version, Himitsu, which I liked even more, it highlighted for me a little of why I like Japanese films in particular, and East Asian films in general. It's a lot sweeter and more subtle. More sad too, casts a wider emotional net. As a matter of disclosure I'll point out that I am not a remake basher, on principle, at all.
The basic story centers on a seventeen year old girl whose body is inhabited by her mother's soul. The two of them were in a terrible accident, and while in the hospital, just as the mother is about to die she reaches over, all ceiling of the Sistine Chapel like, and transfers her soul into the body of her daughter. The daughter keeps her body but becomes her mother in personality and memories. When she goes to school and hangs out with her friends she doesn't really know what's going on, who the people are or what her homework assignments are, because ... well, she's her mother now, for all practical purposes. It takes her a while to come to terms with what's happened and even longer to convince her father/husband.
Now, to cut right to the chase in case you can't see the 400 pound gorilla in the room, once the father is convinced that his wife is living in the body of his daughter and they, well, ya know, they're all in love and stuff ... so what about sex?
Things get a little creepy but I give both films high marks for how delicately the sex question is handled. I'll leave it at that and say it's not the main theme of either film, just one of many issues that come up.
The English version is loud and antagonistic. It's not a horror movie (not sure how it got marketed as such) unless you consider David Duchovny spooning with a seventeen year old girl to be horror. The daughter is in rebellion mode against the mother before the accident and their relationship takes center stage--the mother discovering her daughter's world of sex, drugs, and rock and roll while the daughter comes to recognize the love that her mother has always had for her. The Japanese version is much quieter in comparison. The mother and daughter love each other very much and the antagonism angle focuses on the husband/wife relationship. The husband becomes sad and wimpy, feeling oppressed by having his wife around only as a roadblock to his moving on. The diet of sadness is served in small introspective doses, though, and changes how the film resolves. In the English version the resolution occurs between the mother and daughter. In the Japanese version it is between the husband and wife and involves a big twist that should serve to remind viewers that this has been a fantasy film, after all. As mentioned, I saw the English remake first and it didn't do the twist, and when I watched the original (with the twist) I thought to myself "This is why I like Asian cinema." It is so Japanese. Just when the limits of despair seem to have been reached, another complex layer of sadness is revealed for your weeping pleasure. (I wonder how the book they're both based upon ends.)
I'm not a remake basher but I think if I had seen the Japanese version first I might have railed against the remake for changing focus and tone. Having seen the English version first allowed me to enjoy it for what it was, and it didn't in any way impinge upon my enjoyment of the original. I recommend both films but suggest, oddly, seeing the remake first. Both films explore, and handle, the creepy dilemma of "Would you have sex with your wife if she was living in your daughter's body?" quite well. They're both sweet and touching ... except for some of the touching.