A disappointing experience

There are a group of us who have been taking part in some kind of experiment or experience, it's unclear to me if it was voluntary or not. I am inclined to tell the person in charge of it that the experience was not useful to me, that it was disappointing. The others are fearful about giving negative feedback, as if this might be a dangerous thing to do, and I hesitate, but then confront him. I say that there were times when I thought it had potential and might be becoming interesting but it ultimately failed to live up to my hopes. He did not say anything and appeared to reluctantly accept what I was saying. His posture was slightly stooped and he turned away. I had a feeling of relief that I had found the courage to make my opinion clear and had not been intimidated by him.