Just a quick summary of my observations, maybe others can add their thoughts as well:
- more plugin sources, including complex stuff like e.g. GWT
- good DOM-Model article
- missing many @since 6.0 tags
- missing requested features that were even highly voted in JIRA but still postponed to minor release
- completeness of JavaDoc is still very bad although this was promised to improve massively for 6.0, only some of the new classes are documented, some packages are more or less completely "JavaDoc-free-zones"