“Heroes of Might and Magic V: Tribes of the East”

The expansion will be released as a separate disc and will not require the original game or Hammers of Fate. So, essentially, it's already a separate game, not an expansion. And the number of changes/innovations suggests that Tribes of the East is closer to Heroes 5.5. The official release date is currently September 25th. And support for previous versions (patches, etc.) will continue, so the choice will be which game to play.