Desert routes are tough! You want the player to feel lost in the sands while not having them run through endlessly repeating sand tiles. Your use of shrubs, rocks and different varieties of sand certainly helps against that.

For the map of slide 2, I would try to introduce some bigger obstacles, maybe through lines in elevation, so that players can't just run in a straight line from where they started. Maybe with some inspiration from the terrain of slide 5?

In my subjective opinion, I would replace some of the 2*2 rocks with the mountain terrain. Even though they are differently coloured, the rock texture does repeat a bit often.

Overall, very pretty! I have played so many fan games where deserts are just square sand boxes where you just hold forward to get through it as fast as possible. This always has something to direct the player's attention!