He dresses different than you, he listens to different music and his opinions on a variety of subjects are completely the opposite of what you hold to be true. Even so, he cares what you think ... about him. Whether your teenager says it or not, he wants you to think highly of him. If you comment on the fact that one of his friends is getting a better grade in Algebra class or that his older sibling never had trouble keeping his room clean, you're whittling away at his confidence and making him resent you.
If you can focus your unqualified remarks on the things your teen is good at and the things he or she does right, you'll have a better chance of maintaining a good relationship. Everyone has different strengths and weaknesses. Highlight the strengths from time to time. As crazy as it sounds, teens wish their parents were proud of them.