IMHO - functionality that is needed for this plugin to be 100% wonderful:
-It does not have any reporting. The administrator cannot see who received notifications. The administrator cannot see who should receive notifications.
-It does not include the functionality to CC another email address, such as a teacher/manager or supervisor.
-It does not include any of the "fancy" text editors - Bold, URLs, Underline.....nothing...plain, bland text that does not "catch" a student's eye.