this is the only film on my list that i don't feel stands completely on its own. i strongly recommend that you read the first book in frank herbert's series before you see this movie. this is because the story squashed as it is into movie length, is enormous. therefore if you are not familiar with the details that the novel provides, a lot of the film may soar over your head. if you'd like to dive a little deeper into frank herbert's head, i recommend reading the transcript of an interview he gave in 1969. 
it is a messianic story. set mostly on the desert world known as dune, (arrakis), we follow the son, (paul), of a powerful duke, (leto atreides), as he struggles, all but unaware, toward godhood. the backdrop of the story is filled with the political fencing of the emperor of the known universe, (shaddam iv), some other powerful planetary leaders, (including the duke), and some interesting guilds. two of the guilds that are crucial to the plot, are the navigators and the bene gesserit witches. through centuries of interbreading, the mysterious powers of both guilds are eventually combined in the form of the movie's hero, paul "muad'dib" atreides. 
this transformation is brought about during paul's exile at the hands of the evil baron harkonnen. paul escapes into the deep desert only to find the native fremen who's relationship to the giant sand worms and therefore the spice, (an immortality drug unique to dune), is pivotal to paul awakening. 
this film defies description, as you might be able to tell from my jumbled attempt. however if you have read the book, it is a very accurate translation. i have watched this film so often i fear my laser disk is wearing out.