Very well done! I can tell that you put a lot of love into this. I have some suggestions - firstly, allow pausing! as i write this, I need to hover over the build buttons, as it is the closest thing. Secondly, time scaling would be nice. Third, a menu where I can toggle the music, it is a nice loop, but it is rather short (sound effects are really cool, should let me know how you made them). #4, I think the sand dune humps could use a bit of variation, you already did this with the cacti, just one or two more variations would enhance the feel.
Awesome game!