TCM has an overview. The New York Times says, "within its acknowledged limitations of the modest, low-budget comedy, it is a wholly ingratiating item" and
there is a wholesome ingenuousness about t—a brisk enthusiasm—that makes it unimpeachable. Talk about good, cheap "family pictures": "The Great Rupert" is definitely one.
Wild Realm Reviews calls it
a hoot, a great family film that will by no means bore the adults of the family. Even the crappy stop motion animation for the squirrel was a hoot.