While the movie version of Where the Red Fern Grows is not quite as good as the book by Wilson Rawls, the film is still a quality family film and very much worth watching if you are a fan of the novel.
The changes in the plot for the movie version are minor, and most of the same themes Rawls intended for his readers can be found in the movie. However, one glaring difference is the fact that the characterization in the movie cannot touch the novel. The movie does little to build up Billy's "dog wanting" disease as well as Billy's dogged (pun intended) determination to secure himself some hunting hounds. This takes away from the reader's sympathy for and identification with the protagonist. Grandpa's character also does not come off as well as he does in the novel. In the novel, Grandpa is clearly a wise man despite his one irrational act; in the movie, he seems plain irrational, and there is no sign of his wisdom on the subjects of life and coon hunting. The extent to which the dogs are given characters and personalities in the book is not found in the movie, either. Billy's mother and father do translate fairly well from the book to the big screen, but the fact that the protagonist and his dogs do not is the major weakness of the film.
In closing, if you're a fan of the novel, then you should definitely watch this movie version, but don't expect it to be as good as the classic children's novel.