Why is Massanutten mountain so dramatically different than surrounding mountains?
If you look a wider view from above and a bit to the west, you will notice Massanutten is not that straight nor is it unique most of the surrounding mountains are the same, especially to west. Basically you camera is pointed in exactly the wrong direction to see the other mountains. 

on a geologic map it becomes even more obvious. 


A false color which hides the difference in plant life makes it even easier.


You can picture the appalachians as a flat section of rock that has been compressed like an accordion east to west, that's why they are more or less parallel, but not perfectly parallel becasue the rock is not completely uniform in strength or hardness. Plus the compression has a bit of a curve to it making it even less uniform.