This is mostly a release focusing on improving the new Notifications feature, in order to make it as polished and usable as possible before the end of the year (i.e. before the end of the Cycle and before we elect a new LTS release). It also contains several bug fixes.
Full release notes available at http://www.xwiki.org/xwiki/bin/view/ReleaseNotes/Data/XWiki/9.10RC1/
See http://jira.xwiki.org/secure/IssueNavigator.jspa?reset=true&jqlQuery=category+in+%28%22Top+Level+Projects%22%29+and+fixVersion+in+%28%22%39.%31%30-rc-%31%22%29+and+resolution+in+%28%22Fixed%22%29 for more details