diff -rq /.../folder1 /.../folder2

The r flag assures that each directory is recursively looked at.
The q flag activates the brief mode: without this flag, diff will tell us the actual line-by-line differences for any files that exist in both locations but are not identical.

To check differences between remote shares:

diff -rq /Volumes/Movies-1 /Volumes/Movies-2

This also works with rsync:

rsync -avun $SOURCE $TARGET

In case you want to avoid corrupt files, you want to check for checksums too:

rsync -avnc $SOURCE $TARGET