I don't know why folks are bashing the Gospel of Nicodemus. As LBK as said, the imagery of the Harrowing of Hell by Christ, and the opening of Paradise are concepts found there and are part of our Holy Tradition.
I've been to some parishes that publicly read this Passion Gospel during Holy Week (outside of the services, of course). It's my understanding that the Gospel of Nicodemus has always been considered profitable to read by the Church. Let's not forget that the canon of Scripture established the books that could be read publicly at the Liturgy, not all books that are authoritative in the Orthodox Church. St. Jude, in his epistle quotes from the Book of Enoch, though it does not belong to our canon (unless you're in the Ethiopian Church), and the Old Testament makes several references to books that no longer exist. Many Church Fathers quote from non-canonical books, as do many modern Orthodox scholars (I believe in one of his books, Metropolitan Kallistos even quotes from the Gospel of Thomas*).
Scripture is the cornerstone of our Tradition, yes, but let us remember that around the cornerstone exists the entire building of the Church, and that they former together a single entity.
*Metropolitan Kallistos quotes a section of the Gospel that is Orthodox in its teaching. This is no way an endorsement of the whole Gospel, which is a Gnostic work. Rather, as an Orthodox bishop he is "rightly dividing the word of truth" and speaking with the words of the Gospel only insomuch as it exemplifies Orthodox teaching.