This is a major improvement over the previous beta with many fixes. Part of the reason it took so long was to ensure that the fixes were accurate, and hopefully this will put us back on track to having a stable release really soon.
Most important changes:
All meta tags should load and save correctly again, I'm really sorry this was broken in beta4 :(
Entities now have to have Metatag integration specifically enabled via hook_entity_info, the module will no longer automatically assume all entities need meta tags.
Fixed a potential security hazard which could have lead to information disclosure when the PHP module was used and PHP code was used as a node teaser.
The icky metatag_update_7004 has been replaced with several smaller updates that should not cause as much headache.
Some invalid and empty data will be purged and fixed.
Integration for both the Migrate and Feeds modules.
Added an admin page to revert all meta tags for a given entity or entity bundle to their defaults.
Many fixes and improvements for existing meta tags, e.g. Twitter Card tags should be correct now.
Some new meta tags, including original-source, news_keywords.
Because of the extensive list of changes, please test this before deploying it to a production site and immediately open a new issue if a problem is identified.
Once again this has very much been a collaborate effort, I'm very grateful for everyone's help in making this release.