Nice pictures but I have the same comment: a bit off: dull, plain contrast, brownish. No pizaz!
In three words: probably digital uncorrected.
Have you worked with the pictures in a good imaging program, like Paintshop Pro or Photoshop? Looked at the histogram, twiddled with the colors, etc? Every, yes every, digital picture needs that, am afraid!
And there is far too much. What are the essential diffences between the first 8 Machu Picchu pictures? Why would one be interested too look at them all? Sorry about this blistering comment, but just ask yourself that question
Have a look at:
http://www.vanhulsenbeek.com/Brazil/album0.html and see what I mean.
Though I have had comments about lack of detail in shadows, skies too blue etc.
There is always a pay off, as anywhere else in life
Best regards Sander Amsterdam