I had an inspiration for a new retrospective format that I have run and a couple of colleagues have also. (So it’s a few iterations in already.)
On a whiteboard or wall space you create three columns with the three arrow images in the title position as shown.You start with the first column on the left. Ask the room - "what do you know now that you didn’t know at the start of the sprint?" - and the room populates this column with sticky notes. Then group and discuss.
Now move to middle column. Ask - "if you could go back in time to the first day of the sprint, and knowing what you know now, what advice would you give yourself?" Again the team populate this column with sticky notes. Group and discuss.
The third column is - "given the information we have just collected, and anything else that you can think of, what you want to take forward into the next sprint?" At this point the team can move items from the previous columns over and/or add new sticky notes. Group and discuss.
Finally we dot vote on the items in the right column and turn them into action items.