The highlight of Drush 6 is the new outputformat system. You can now request Drush output in easily parsed formats like json, csv, ini, etc. See https://github.com/drush-ops/drush/blob/8.x-6.x/docs/output-formats.html
Note: if you are using Drupal 8, you should stick with a frequently updated clone of master branch. Drush 6 supports Drupal 6+7 but not Drupal 8.
Significant changes since 7.x-5.9 listed below. Note that the numbers below map to our old issue tracker at http://drupal.org/node/[n].
- #1255708 by greg.1.anderson, kid_icarus, rickmanelius: Use quick-drupal with drush make
- Enhance help command with --format option. You may now get the full command definitions for all available drush commands in json or * var_export formats.
- #1829596 by greggles: Added ULI needs a turbo.
- #1649598 by greg.1.anderson: Bring drush_role into Drush core
- #1829596 by Owen Barton: More turbo - more flexibility in parameters, path redirection, browser detection/opening.
- #1715184 by jonhattan: Run tests on drupal any major version of Drupal.
- #1548034 by greg.1.anderson: Show permissions defined by a module after pm-enable, and in pm-info
- #1882426 by greg.1.anderson: Document new environment variables PHP_INI, DRUSH_INI and PHP_OPTIONS.
- #1866344 by greg.1.anderson: Implement output format engines
- #840540 by torotil, izmeez, igor.ro, christopheperrin, noels, girishmuraly, paul.lovvik, skwashd, Garrett Albright | expandonline: Added * Specify a patch from local file system.
- #2017189 by moshe weitzman: Added Option validation for --backend requests.
- #2010042 by clemens.tolboom, helmo: Added Use composer to configure the test environment.
- #2020291 by Grayside: Added Move support for desktop notifications into Drush Core.
- #698264 by posulliv, scor, juampy, Wim Leers, dalin, greg.1.anderson, moshe weitzman: Added Better handling of structure-tables and skip-tables options (including cache_* support!).
- #2012362 by Steven Jones: Added Use fewer subprocess during make.
- #1206340 by joestewart, greg.1.anderson, leewillis77, drzraf, jhedstrom: Added introduce an options array in the root level of the makefile.
- #1991764 by Damien Tournoud: Added Support using a distribution as core.
- #1364814 by eiriksm, jonhattan: Added Extend pm-enable to offer downloading the project for missing extensions.
- #1792550 by RobLoach, jhedstrom, lotyrin: Add composer.json so that Drush can live on Packagist.
- #2041109 by greg.1.anderson: Make Drush call command hooks more consistently.
- #2031383 by ergonlogic: Added Provide weight-like mechanism to ensure order of hook calls.
- #2027165 by dawehner: Added the --druplicon global option. Try it!.
- #2020957 by Aron Novak: Complete: use shell fallback