Though "Gwen (Le livre de sable)" isn't very animated, it's all about atmosphere and beautiful visuals. Even if it's paper cutout, most of the animation is made by redrawing characters every frame just like traditional animation, except everything is shaded all the time, with a particular texture to it.
The world in the film is a imaginative fantasy, mixing surrealism, middle-orient and a bit of science-fiction. It's not a character driven film, they are somewhat flat and just part of the pretty picture. The story is vague, very mysterious and you interpret it the way you want if you feel the need to, though there's very apparent references to religion, the Bible especially, and materialism. In my opinion, the film lacks something to care for, as you are left confused about what's going on for a good while. The slow pace, which otherwise is absolutely perfect for the film, doesn't help you to feel good when you are confused. The voice acting is very neutral too, they have no emotion, which kinda fits the style but doesn't help the bland characters.
The Story tells that a long time ago, the gods went away, but they left a mysterious thing which at night lay stuff around the land. These things are giant beds, sinks, clocks, etc. When two young people decides to stay out for the night, one is kidnapped by the thing, and the other, with the mother of the kidnapped, go to find the thing.
Watch it if you liked Laguonie's shorts (I sure do). Or if you like surreal films, experimental and not-only-for-kids animation. It got it's defaults, but it's worth a look.