In most cases you aren't so much writing to the author as to other potential readers. Very few authors are going to take your reviews to heart (even the good reviews!). It's a professional skill to build a thick enough skin that the reviews don't get to you (if they did, you wouldn't get far in a business that is 99% rejection). That said, it's still thrilling to know people are reading what you write (no matter what they say...but, again, hopefully good things).