In my experience code reviews need to be a conversation. I'm on a small scrum of 3 developers and we all review each other's code. The major thing I've learned is that you need to depersonalize the code. Don't ask "why did you do this", or "you did it this way two weeks ago and now it's failing in production". It's all about the we. I say we so much in my code reviews you'd think I was French. Also, I really try to make my tone seem more of someone who wants to learn vs. someone who is criticizing.