[noggin]

What is 3D ISO exactly anyway?

3D ISO is a disk image of a 3D Blu-ray. Because of the way 3D Blu-ray works you can't rip 3D Blu-rays to a Blu-Ray folder structure and guarantee 3D replay, instead you need to rip them as an ISO disk image. This is why ISO is a big thing for 3D. (The other alternative is to rip the BD to a 3D MVC MKV - using third party software)

(A folder rip copies the files, an ISO rip copies the filing system. Because 3D Blu-rays do very clever things with the UDF file-system to allow for 2D compatibility without duplicating content, you need to retain the 'UDF-ness' - which is why a folder rip doesn't usually work)