The full changelog is available at http://crux.nu/svnweb/CRUX/view/crux-2.2/ChangeLog.
Starting with shadow 4.0.15, useradd's defaults for the primary group has changed. If you're updating from 2.1, be sure to merge login.defs, which is rejected by default.
The pkgconfig port has been renamed to pkg-config. If you're updating manually (i.e. not using setup from the CD), you'll want to edit the respective line in /var/lib/pkg/db.