From the diff man page:
-q
Report only whether the files differ, not the details of the differences.
-r
When comparing directories, recursively compare any subdirectories found.
Example command:
diff -qr dir1 dir2
Example output (depends on locale):
$ ls dir1 dir2
dir1:
same-file different only-1
dir2:
same-file different only-2
$ diff -qr dir1 dir2
Files dir1/different and dir2/different differ
Only in dir1: only-1
Only in dir2: only-2