It is more important to tell them what is wrong so they can improve. These answers are all true, and they are all stupid. We are not dealing with machines, we are dealing with people. We have to tell them that we appreciate their efforts. The negative outcomes are worse if you don't tell them.
Criticism focuses on the past, has a personal focus, has a negative tone, and is problem oriented.
Constructive feedback focuses on the future, centers on the actual behavior, sets a positive tone, and seeks a solution. The most powerful human relations tool I have ever used. Use it to tell others when they have done a good job. When you put in extra time on this project, I feel like you are really committed to the team effort, I would prefer that you keep up the good work.