Even if students are buzzing with anger, make sure they begin with the positives. There are bound to be some - if there weren't, they wouldn't still be with the course. The circle approach ensures each student has a chance to speak. For each point, check how the student thinks it affects their learning. This can often be very enlightening.
Honest comments are more useful than diplomatic ones.
It is important that individuals do not feel that their comments may make them vulnerable. Attached is an explanatory handout which you may like to customise and to give participants.