The main user facing change is that "drush civicrm-cache-clear" has been replaced by integration with the standard drush cache-clear command. You can see it in the options by running "drush cache-clear", or call it directly (this time using the alias "cc") using the command "drush cc civicrm".
There are also aliases added for a number of commands, which should save a few keystrokes. You can examine these using the command "drush help --filter=civicrm".
There are also a number of changes to the code structure - the command callbacks now use the standard conventions making it easier for you to add your own custom pre/post hooks, validation routines are also separated from the main callback. Output (stdout), error/log messages (stderr) and exit codes should also now be more standardized and machine parsable.