If you already own the previous edition of the Nag Hammadi Library in translation, and are wondering if it is worth it to buy the new edition—it is.
The Nag Hammadi Scriptures is more than simply a new edition of the old work, it is in many ways a different book altogether. The contents will be familiar from previous translations, though more readable and less technical in many word choices. Many of the names familiar from the previous edition where involved with this edition.
The formatting in the new edition is a vast improvement. It makes the text more readable, and it is easier to find the passage you are looking for. It includes actual footnotes, a very useful formatting feature too often replaced by pernicious endnotes. The end commentary material now consists of short overview essays on the various traditions within the larger Gnostic tradition.
The new edition also includes Coptic texts found after Nag Hammadi, such as the Gospels of Judas and Mary Magdalene. Although for texts found before Nag Hammadi you will need to refer to the older editions by G. R. S. Mead. (Perhaps I should say “the venerable Mead.”)
Unlike some other collections of scriptures that you may read through and then shelve, this edition is the one you will keep close at hand. My copy has already become a frequent companion.