Notepad gave me loads of gogglegook when I uploaded one of the files.
Open it in a plain text editor. XML files are really suppose to be reader friendly. They are meant for use as configuration files, and other such things.
You can try an XML reader like http://codebeautify.org/xmlviewer , though.
If you want to edit or view .xml files, right click on the file and click "Edit with Notepad++". If you want Notepad++ to be the default viewer of .xml files, then you need to go to "Control Panel/Default Programs/Associate a file type or protocol with a specific program", scroll down to .xml, double click on it and choose Notepad++ from the menu.
A tree view is about the best you're going to get. As I mentioned before, XML isn't really meant for reading.
Notepad++ has a tree view.