Having never been a Roman Catholic, I would really be unable to compare the two. I do know that in Orthodoxy, just as a previous poster has written, it is not simply about God's forgiveness (though it is about that too) it is also about the healing of the soul.
In an excellent little volume entitled The Forgotten Medicine: The Mystery of Repentance by Archimandrite Seraphim Aleksiev, it mentions that, "When we go to Confession, we enter Christ's infirmary.(emphasis is in the book) Here God Himself is the Doctor, because only He can give and take away life, judge and acquit, punish and forgive. The priest is only a witness and a representative of God.... The priest examines our soul, but God will heal it."
I always rack my brain, trying to remember the vast multitude of my sins. In the Russian tradition, we generally pray the Confession prayer of St. Dimitri of Rostov, including our own particular sins, which concludes with something to the effect of, "I also repent and ask forgivness for all those sins which I do not remember because of their multitude and my own negligence."
I think when it comes to all the mysteries, we must always remember that which seems forgotten in the West: that we are dealing with a Person. God, who knows our intentions and remembers that we are dust, is merciful.