We have all seen these book-to-movie adaptations that are nothing like the book. Sure, the characters and setting, and maybe even a few plot points are the same; but almost invariably something is changed, removed entirely, or even added. Creative license does tend to go too far (I, Robot, directed in 1994 by Alex Proyas, being the premier example). However, this is not always the case. There are times when changes to the original story line have actually benefitted the movie, and William Wyler's 1949 film, The Heiress' take on Henry James's 1880 Washington Square is one of those times.
Washington Square tells the story of Catherine Sloper, the daughter of a well-to-do doctor who falls in love with Morris Townsend, a man Dr. Sloper does not approve of because he believes Morris is after Catherine's money. The Heiress tells the same story, but with a change here and there, and none of these slight changes alienates it from the novel it is based on because they do not upset the story line. It does not matter that Dr. Sloper (Ralph Richardson) and Catherine's (Olivia de Havilland) conversation in Europe takes place in a café instead of on a cliff, and it does not matter that when they come back from this vacation that Dr. Sloper can find actual evidence of Morris's (Montgomery Clift) presence rather than just sensing it. It still works.
There is one major change noticeable to all who read the book and saw the movie, and that is the ending. Washington Square ends with Morris coming back (after having deserted Catherine earlier) and Catherine rejecting him because he is not the same Morris she knew. The Heiress, however, ends with a bitter Catherine exacting revenge on Morris by standing him up in the same way he did to her years ago.
Both endings are well-suited to the story, and I do not believe that The Heiress' ending is any better or worse than Washington Square's. That choice is the viewer's to make. Whether Catherine's eventual rejection of Morris is subtle or blatant does not matter; each shows how bitter she has become over the years Morris is gone, and each does a great job of showing this.
While, in my opinion, creative license has broken its share of films, I believe it has actually enhanced this one.