This retrospective switches the attention of the team from the sprint they just had and allows them to explore what their 'perfect' sprint would look like. I have used this with teams that had a bad sprint - topics from the sprint will surface irrespective.
We represent the sprint as 4 columns - Prep, Planning, Dev Day, Review. You can choose the columns you want to focus on. The team then write up stickies for their perfect sprint, focusing on a column at a time. You will find that opposites occur at this point e.g. the opposite of what actually happened in this sprint. You can pose questions to get to the root cause and add more stickies if required.
I usually pair people for this, which seems to work better that everyone individually participating. I allow a time box of about 5 minutes and then we quickly go through the points raised. You can group common themes at this point. We repeat this for each column in sequence, following a journey through the sprint.
At the end we start to highlight what is in our control. This is usually pretty high - 50-75% seems to be about right. This leads the team to the obvious question - why don't we have our perfect sprint more often, given so much of it is in our control?
This outcome drives which actions we want to take into the next sprint - taking one from each column is a nice idea, but it does depend on what you came up with.