The RGNT differs from standard UBS/NA Greek texts in a number of places. The original first edition was based on the Greek text underlying the New International version of the Bible. The copyright page of the RGNT2 contains this statement:
The Greek text used in this edition of the Greek New Testament was originally developed for the Portland Index Project by Edward W. Goodrick and John R. Kohlenberger III, and subsequently reviewed and modified by Gordon R. Fee.
The first edition contained the same statement, but without the mention of Fee, which makes for speculation that Fee, a member of the TNIV committee had a hand in modifying this new edition which is based not on the NIV text, but rather the TNIV. There's also a brief forward by Fee immediatly following the title page.
What many people don't realize is that the so-called "standard" Greek text is an amalgam of readings from many different ancient manuscripts in an attempt to sort through discrepancies and find what is probably the original reading. Many people may not also realize that often strong cases can be made for the reading of another variant over the one accepted in the standard text. Almost all English translations have readings in which a variant has been chosen over the "accepted" text. In the past, unless one chose to compare a translation very closely and systematically to the Greek text, there was no way to discover how many places that a translation committee chose to follow a variant text.
When the first edition of the RGNT was published, it was based upon the NIV and it listed exactly 231 places where this translation diverged from the standard text. This new second edition has been modified to match the TNIV, and according to the introduction, 285 divergent readings are found in this translation. Everyone of the divergences are indicated in the text at the bottom of the page in both editions.
Until now, it's been very interesting to compare translation renderings between the NIV and TNIV texts. Now, however, we have access to something more interesting--the underlying Greek texts themselves. Now we can spot and confirm alternative readings such as that found in Mark 1:41 which I've written about on This Lamp.
I'm also pleased to see Zondervan make a bold step away from the NIV and to the TNIV as it is time for the older to become "lesser" and the newer to become "greater" (to borrow from John 3:30). I've suggested to my contacts at Zondervan that should consider publishing a diglot containing the RGNT2 text on one page with the TNIV on the facing page.
If you're interested in further information about the second edition of the Reader's Greek New Testament, see my full review at This Lamp. I welcome all of the new features except the new typeface, which I don't care for any more than I did that of the original.