This movie is a bit of an acquired taste. It took a few viewings from me before I could get past all the weirdness and thoroughly enjoy it.

The first time I saw it I was fifteen, and I did't get much but I was pretty fascinated by the world of the film - so I went and read the novels, and they were very satisfying. Even if they had some misogynistic overtones, Frank Herbert's writing had great vision. The themes of invading a desert world for its precious resources and the war over dominating it, as well as abuses of the native populations and the motivating effect of religion ("Deserts, traditionally, are the wombs of religion." goes a Bene Gesserit saying) are no doubt relevant to modern audiences as they were when Herbert wrote as a journalist.

A story like this could only have been done justice as a TV series, not as a two or three hour movie. Nevertheless, David Lynch did some magnificent stuff with it, even if he didn't like it himself. The Bene Gesserits are utterly fascinating, the Harkonnen are really frightening in a sort of surreal way, the Mentats also are interestingly portrayed (I so enjoyed Brad Dourif as Piter); even the Guild Navigators, incredibly weird looking, made you interested to learn more.
The special effects, though fantastic for 1984, today seem awful and forced, and spoil the film for modern audiences, and that's a shame.