The story takes place more than 20 000 years in the future, where the universe is ruled by the Padishah-Emperor Shaddam IV. Shaddam's Imperial forces are matched by the Landsraad, a collection of noble families designed to stand against the Emperor only as a whole(if necessary). The third main group is the Spacing Guild, a neutral force who is responsible for space travel. This entire system is based on the drug known as the "spice melange" that provides long life and precognitive powers yet is highly addictive. The drug is vital for the Guild Navigators so they could predict where they are going(so they wouldn't crash into a star or nebula). The spice melange exists on only one planet in the entire universe and cannot be replicated via artificial means. The planet is Arrakis, also known as Dune.
The story begins on Caladan, the ancient home of House Atreides(the good guys) who have just been offered by the Emperor to take over Arrakis. Despite knowing that the Emperor is likely plotting against them, Duke Atreides is forced to take over Arrakis(political stuff). Meanwhile, the Bene Gesserit(a sisterhood who uses natural genetic engineering, basically giving birth, giving birth, giving birth over thousands of years in order to create the ultimate male: the Kwisatz Haderach who could clearly see the future and be the most effective ruler of all time) are testing the Duke's son Paul(main protagonist) to see if he is the One or not. They don't give a clear answer and anyway, we don't need one.
So House Atreides moves to Arrakis and is betrayed by the Emperor and House Harkonnen(bad guys) who attack them and murder most of them. Paul and his mother escape to the nomadic Fremen who live in secret in the deserts of Arrakis and eventually rise to become their leaders. Using the Fremen, they take back Arrakis. No more spoilers.
The complexity of Dune is astounding. The universe that FH creates is both believable and unbelievable. Judging from the dialogue of the characters, everyones IQ's are in the 1000s in the future and their conversations ALWAYS have hidden meanings(simple talk doesn't exist in the future). The psychic part of the human brain seems more developed due to the effects of spice and thus there is talk of future vision. Unlike the later Dune novels, this one deals with the symbolism of war, religion, psychology, parapsychology etc. etc. etc.
Due to the endless meanings within meanings within meanings, it is harder to relate to the characters than one thinks and I honestly had trouble trying to figure out who was good and who was bad, because I never understood what they're really thinking about. This might've been Frank's way of showing us that the universe isn't black and white, there are grey people too.
Dune is something that cannot be adapted without losing 95% of its meaning and thus, neither the 1984 Dune nor the 2000 miniseries gets close(though both were great attempts and were brilliant in their own ways).
Do I recommend Dune? Only to brainiacs and sci-fi fans, because this is a hard read. A hard, but ultimately satisfying one.