Of course using 'I' instead of 'you' is a good way of criticism but Thomas Gordon says 'Even if you serve your message as a sandwich the person who is listening to you picks the sentence you want to say so it is not useful indeed,instead of it by using 'I message' you can say your ideas or feelings about the job directly,such as 'I liked your introduction part,but I'm not sure about the rest,or I'd expect a better one from you..''