peer review

I thought the peer review was very helpful. But I also felt uncomfortable doing it, because i'm afraid to say to much. One reason i'm afraid is because english isn't my strong point so i don't always know if what i'm saying is correct. Another reason is i'm afraid of what the author is gonna say back to me. Is he gonna think im mental? Is he gonna punch me in the face because i don't like something he wrote? Don't get me wrong peer review isn't always bad, I personally find it very helpful for me, because someone usually points something out to me that i missed. So like everything else in life it has it's pros and cons!