Microsoft now provide and allow (officially) direct link for downloading their Windows 10 operating system from their Web site without any subscription.
Prior Windows 10, ISO download was reserved to the store purchase and Service Providers Level Agreement (SPLA).
Follow this link to get the official Windows 10 release : http://www.microsoft.com/en-ca/software-download/windows10ISO
This will allow you to create a bootable USB flash drive or DVD.
If you are accessing the site using a Windows machine, it will let you download a tool to generate the ISO. If using a non-Windows computer (Mac OSX, Linux, BSD), it will let you download the ISO image directly.