Create a big scale (i.e. a long line) on the floor with masking tape. Mark one end as 'Great' and the other as 'Bad'. Let participants stand on the scale according to their satisfaction with the retrospective. Ask people what they notice.
Psychologically, taking a stand physically is different from just saying something. It's more 'real'.
See activity #43 on how to begin the retrospective with the same scale.