First off, directory listings are now nodes. This means permissions can be set using standard node access modules. Also means additional data can easily be tacked onto these nodes. Also, many features in the 5.x branch were readded that were lost in the transition to 6.x. This includes directory structure being displayed as breadcrumbs, sorting by name and size of the listing, and description file support. File blacklisting was added with support for UNIX-style private files (ones that start with ".").
We've been in -rc long enough, plus the Drupal 6 port of filefield finally needs to be tackled. Therefore, some final polish and one nice feature compared to the last release candidate.
You get all the features and bugfixes from rc1 (doesn't have a release node), rc2, rc3 and rc4, plus these three additional improvements: