Eternal Sunshine of the Spotless Mind is one of my all time favorite movies (I am a Charlie Kaufman nut). It is about a couple who each independently decide to use a strange service to erase the other from their memory after a difficult breakup.
It takes place in several time areas - the present where Joel and Clementine find themselves in Montauk, unsure why, and meet, seemingly for the first time -- Joel before and during the process of having his memory erased -- and Joel's mind during the procedure as each memory is experienced as it is deleted. In the first time area, the present, there is a strange numbness to their interactions; during the process of having his memory erased there are sort of complicated side stories about the people performing the procedure that in the end become very important. Much of the movie is in the memories themselves, going backwards in time, starting with tense and upsetting interactions during the demise of their relationship, then moving back to more fun and loving ones, as Joel begins to panic at the thought of losing them.
Eternal Sunshine of the Spotless Mind has an unpleasant nerve racking feel, kind of like being in someone else's panic attack. The relationship between Joel and Clementine is not a good one -- she is frequently mean to him and his passivity is both maddening and heartbreaking. It's not that you want them to get back together. Instead you experience that terrible sense of loss and desire to retrieve a lost love, and to preserve something of it.