Steve Berczuk writes a short and succinct article on TechWell describing, "Why Agile Retrospectives are Important in Software Development." I'm looking forward to reading the comments and responses he gets.
More and more I think of Agile Retrospectives as an opportunity for the kind of learning that leads to real adaptive action in complex situations. I'm also looking forward to the publication of Adaptive Action: Leveraging Uncertainty in Your Organization by Glenda Eoyang and Royce Holladay. Adaptive Action is a close cousin with our flexible framework for designing retrospectives.
If, as Steve describes, you want retrospectives that generate valuable learning, look for just enough structure in the group process design to help team members learn, think, and choose useful improvement experiments.