A comparison between the play an the movie is given in this review by Richard Alleva.

I reviewed the stage play, Shadowlands, three years ago (Crisis February 1991), praised it, but issued a warning that I now repeat re Richard Attenborough's film adaptation. "Let devotees of the life and works of Clive Staples 'Jack' Lewis go to ... Shadowlands .. . forewarned though not necessarily forearmed. If they go to sniff out omissions and distortions of facts, they will have a field day. But they won't have as good a time as those who attend the play to discover what idea, what compelling image the playwright William Nicholson perceived in ... Lewis's marriage to Joy Davidman, and how close Nicholson comes to realizing that image theatrically."

The stage version is made of sterner stuff than the new film. In the play's first scene, Jack Lewis, delivering a lecture, addresses the question of...