aptitude has a very advanced search system which allows you to look for anything you may want.

Here is how to find missing recommended packages:

  1. # Explanation: we are looking for broken reverse dependencies
  2. # of type “recommends” for installed packages.
  3. aptitude search '~RBrecommends:~i'

To install them (and mark them as installed automatically):

  1. aptitude install '~RBrecommends:~i'+M

Documentation.