Check out his web site www.exceptionalmarriages.com
You can listen to his daily radio show by podcast.
You can purchase one of his books to know what he is about.
I have read his books, listened to his radio shows and his EWTN audio series. I have found that his approach is solidly Catholic. Popcak refers to Theology of the Body and integrates this with modern psychology. While doing this he does not compromise Catholic truth or let people off the hook to follow their own ideas if they are against the Church.
Popcak is strongly anti-contraception and fully embraces the Catholic teaching on marriage. If you want solid Catholic marriage advice and counseling, go to this guy. If you want someone to affirm your own ideas and tell you that you are right and justified in whatever your own approach and belief is, the go to someone else.
Popcak does a lot of phone counseling. He has talked about how successful this is and has cited secular studies confirming the effectiveness of phone counseling.
Although I have not used him for counseling, nor do I know anyone who has used him, I can find nothing that would prevent me from using him. I respect him because he seems to be a man of principle that tells it like it is.