I definitely think games don't necessarily have to be "fun" to be good and even a painful experience can be great in the right context. Still, I had trouble with this one.. the walking was just too slow for me.
That said, I did have moments where I thought "It's just over this dune" and then realizing I still had much further to go and also moments where I got lost even before the sand storm really kicked in, which is a neat thing to make your players experience.
And the sand storm was really cool, I really liked how quickly frames of reference disappeared. Oh and the music was great!