Timelessly true to life
I feel that even though this film came out in the 1960's it can easily translate to modern times. The issues and situations that Joanna and Mark must face are something that I believe that people in relationships often face--and whether you have been married or not, I would venture to say that people who have even been in a long-term relationship could find common ground with these two characters.
The realism in which Hepburn and Finney project into their roles just makes it that much more affecting and real. I love this film, and I hope it comes out on DVD soon.