Well over 3000 years ago, in Children of Dune, Leto, son of Paul Muad' Dib Atreides, grandson of Leto Atreides, and in the full possession of the memories and experiences of all of his ancestors with no exception, lets Sand Trout crawl over his body and form a second skin.  At first it gives him amazing strength and stamina, later his body slowly transforms in some kind of pre-sandworm, a transformation still in progress at the moment this 4th Dune novel starts.  Leto is unique in the entire known universe, not only since he is the only one blending sandworm and human in one body, but also because of the amazing insights he as the perfect blend of genetical optimization during many generations combines with the millions of ancestors offering him every memory, every experience he needs.  Being unique though is being lonely too, and Leto longs for a surprise, something he hasn't expected.  And he knows quite much in advance, since now that he has his own built-in Spice-factory in the sandworm's body, the constant availability of the Spice lets him foresee almost everything.  He has to, the reason he chose the Sand Trout so many centuries ago is that it was the ultimate sacrifice to reach the Golden Path, the only route into the future that allowed mankind to survive.

He has high hopes for the people that surround him right now.  Siona, an Atreides like he, is the first who doesn't leave a footprint in the future.  Duncan Idaho, a ghola (clone) of the original one that died when Leto was small, and the umpteenth ghola made for him in all those years, reacts as predictable as a ghola is supposed to be, and will hopefully do what Leto expects from him.  And meanwhile Leto will have to keep all the forces in that big universe under control to keep mankind on his Golden Path, something that's easier said than done since some have found ways to hide things from him.

He has one weak spot, and that is discovered.  The lovely Hwi Noree steals his heart, but her manufacturing was better than her builders thought it was.  Still, dangers lurk around the corner, unexpected dangers...

This is the third time I read the Dune chronicles.  The first time I read a series of adventure-novels.  The second time I discovered the politico/religious struggles.  Now I can't help noticing the very interesting phylosophical questions asked.  Who knows what I'll find at a future re-read.
It says something about the high standard of this series.  Not many novels can be read -let alone be enjoyed- at so many levels, and Herbert maintains this through his entire series.
So much the opposite (in my humble opinion) of the Matrix, something I had to think of when Leto explained the alternative to his Golden Path.  Where the Matrix (most certainly the latter two) attempted to add a phylosophical layer to its adventure, Herbert actually succeeds.  And in a far more subtle way, woven into the story, delicately tought in every conversation, painted with big daubs in Leto's musings.

It sounds as if this is a Heavy Story: on the contrary, that's just the genius of Frank Herbert.  You can still read this as an adventure story and forget about the questions asked.  You'll find 3D characters, real people in real situations.  You'll find some fighting, some scheming, a little romance.  You'll even find a little humor here and there, far too little though.  If I have to look for something negative, I'd vote for the dead-seriousness with which everyone goes through life.  But to find something negative I had to look hard...;-)