There is a scene in The Big Chill where William Hurt is watching a movie on TV and Tom Berenger comes in and starts pestering him with all these questions about what is going on in the film. Annoyed, William Hurt simply tells him, "Sometimes you have to let art flow over you." I always think of that line whenever I watch Dune. For maximum enjoyment, let the art flow over you; don't overthink it. David Lynch's film is a narrative mess -- incomprehensible if you're walking in cold -- but it is beautiful to behold as a strange piece of sci-fi art. If you want to understand the story of Dune, turn to the book by Frank Herbert. It is well worth the effort.
Lynch's 1984 film version of the beloved book was not the first effort by a director to turn the "unfilmable"story into a movie, but he was the first to succeed in actually completing and releasing it on the big screen. The result is deeply flawed, a commercial and critical failure, but it has since gained something of a cult following. Ask a room full of David Lynch and/or Frank Herbert fans about Dune, the movie, and you will likely get equal parts groans and gushing praise.
The movie is a seriously earnest effort. Unfortunately, there is such a bulk of information to convey that to prevent it from being ten hours in length, Lynch relies heavily on exposition in the form of urgently whispered internal dialogue. Many of the proclamations made by the characters seem important to everyone...except the audience. When Dune played in theatres, they handed out a glossary at the box office to help movie-goers navigate the story, just to give you an idea of the sheer scale of worldbuilding going on here.
In an extremely insufficient nutshell, Dune takes place in a galaxy ruled by an emperor. Noble houses rule different planets, and the film focuses on two of them: House Atreides and House Harkonnen. House Atreides is in the process of taking over the Harkonnens' old stronghold on planet Arrakis, a.k.a Dune, the desert planet. The changeover is part of a scheme cooked up between the emperor and the Harkonnens to trap and destroy the Atreides. Dune is a valuable planet because it is the center of melange, or "spice", production in the universe -- a substance which endows humans with expanded mental capabilities, and which also allows the mysterious Spacing Guild members to fold time-space for interstellar travel.
The heir to House Atreides, Paul (Kyle MacLachlan), may or not be a messiah, and his abilities as such are tested by an order of wise women called the Bene Gesserit. After House Atreides falls to Harkonnen invaders, Paul and his mother join up with the native inhabitants of Dune and lead them in revolt against the emperor.
Let's talk about what Dune does well. First, the cast is great. You've got an absolutely bonkers performance by Kenneth McMillan as Baron Harkonnen, flying around in a heli-suit and covered in oozing pustules; the always wonderful Patrick Stewart, who seems like he wandered onto the set ready to do a Shakespeare play and realized it was sci-fi; and a truly bizarre Brad Dourif as a human computer. A parade of familiar faces make up the cast: Jurgen Prochnow, Max von Sydow, Linda Hunt (briefly), Everett McGill, Sean Young, Richard Jordan, Dean Stockwell, Virginia Madsen...and let's not forget Sting in his evil rubber undies.
Where the narrative fails, the production design and the score work together to make this a stunning gothic/sci-fi experience. The emperor's chamber alone is an Art Deco fantasy. Some sequences are flat-out jaw-dropping, such as when Paul Atreides rides a sandworm for the first time (of course, making allowances for '80s era technical limitations). Press pause at any point in the movie and the frame in question would make a gorgeous heavy metal album cover.
Even if you love it, Dune is not an easy sit. It is cold, dense, distant, and inaccessible, partly due to the source material, and partly because that's just the sort of film David Lynch generally turns out. It doesn't hold your hand and guide you gently through its twists and turns. It's like you've just transferred to a new school and have to jump midyear into trigonometry and catch up or be left behind. I appreciate that it doesn't patronize you but lets you decide if, and to what extent, you want to plumb its depths.