Fine acting, wonderful scenery, and a very pleasant approach to the classic tale make this quite an enjoyable film. Though the character of Fraulein Rottenmeir is a far cry from Johanna Spyri's, as is her relationship with Herr Sessemann, this change may be appealing for those who wish to share the film with children, who might be troubled by the original.
My reason for witholding a top rating is that, as a lifelong fan of Johanna Spyri's "Heidi," I noticed that some of the key themes in the original are missing. Heidi's simple faith, and her faith's being strengthened despite the time of dreadful homesickness and mistreatment by the governess in Frankfurt, do not come through clearly. The plot has been revised so that Herr Sessemann is an uncle, Fraulein Rottenmeir a lovely lady, and Klara (in the book, a gentle sort crippled by over protectiveness) a bit of a brat. Heidi remains in Frankfurt because she feels she owes it to Klara, who tends to move her legs when Heidi angers her.
All told, nonetheless, this is a very well acted film with a great deal of charm.