You can enable free-form comments for each criterion in the rubric.
Click the Assignments link.
Click on the assignment title to open the assignment you want to evaluate using a free-form comment based rubric.
Click the pencil icon to edit the Rubric.
Click the I'll write free-form comments when assessing students check box
Click the Update Rubric button.
Click Grading Tool button.
Click the View Rubric button.
View the rubric with free form comments enabled. If you saved the comment for reuse, you can find the comment in the dropdown menu.
Student view of a free-form comment rubric.