Personally, to me texturing is the most important part of a good map next to terrain; but I feel that it can also be the hardest part for many reasons: You have to be able to know which textures can complement each other well (it's not really a problem unless your making multiple maps, you don't want to use the same old sets over and over again), you have to be patient because it takes by far the longest time on the map, you have to be able to texture good which can be extremely hard to beginners.
However the payoff can be great, when a map is textured well it just stands out from everything else and feels great to look back and reflect on when it was made.
