“Should have” ties to the past. “Next time” maintains momentum.
“What worked” and “What didn’t work” is better than “What went wrong?”
This is the beginning of de-constructive conflict, a type of conversation that holds that there is rarely an absolute right or wrong way to do things, and recognizes that no two people see things exactly the same way. It creates a context for learning that criticism rarely does, even when it is given kindly.