Well, I'd hate to sound a sour note, but there is no reason to consider this as anything other than a modern apocryphon. The book portrays the "translator" Edmond Bordeaux Szekely as a biblical scholar, but the first thing a real scholar would do is publish an editio princeps of the Aramaic text itself and describe in detail the circumstances of the discovery and the MSS. It is almost inconceivable that a discoverer of an ancient text would refrain from publishing the text itself (which would be of intrinsic interest to both Aramaicists and scholars of the NT), but simply produce only an inferior translation and say next to nothing about the MSS themselves (such as the paleography, condition of the manuscripts, cataloguing information). In fact, Szekely claimed to have also found an Old Church Slavonic version of the same book, so there would have been all the more reason for him to produce the text in both languages (especially to note textual variants between the two MSS, cf. the title page of the 1981 edition: "The Third Century Aramaic Manuscript and Old Slavonic Texts Compared, Edited, and Translated by Edmond Bordeaux Szekely").
Szekely claimed to have "edited" the original language texts and because he continued to "translate" and publish new material over the years (in 1937 he claimed that he translated only an 8th of the total Aramaic, whereas in 1977 after releasing new volumes of the text he claimed that he had translated a third of the text), he would have had to have copies of the Aramaic and Slavonic if his work was not a hoax. He was repeatedly asked over the years to provide the details of the MSS he discovered and he promised to do so, but when in 1977 he finally published The Discovery of the Gospel of Peace: The Essenes and the Vatican, he only devoted a single paragraph to discussing the source and the discovery itself (p. 54).
This behavior however is expected if no such Aramaic text existed. It would have been very difficult (if not impossible) for a non-specialist to write a lengthy book-length text in ancient Aramaic without committing lexical, grammatical, and stylistic errors that would have easily exposed the hoax. Even if he had the ability to read Aramaic as he claimed, it takes a whole different set of skills to write in another language with full fluency and naturalness -- plus he would have to avoid making anachronisms. And if that isn't enough, producing an actual forged MSS (or even photos of one) would have involved an additional body of linguistic and egigraphic skills that would be very hard to fake. It is also worth noting that his 1977 edition contains a photo of Aramaic MSS but it is actually a mirror image of the Qumran Copper Scroll (first published in the 1950s); it is disingenuous to present this as a photo of the Vatican MS. It is also worth noting that a skeptic in the 1920s wrote to both the Vatican Archives and the Royal Archives of the Hapsburgs to see if he could find the MSS; he was told on both counts that no such MSS existed in archives' holdings. He was also told by the Vatican Library archivist that Szekely's name does not occur in the register of scholars admitted to the library. There are some details of this here:
http://essenes.net/index.php?option=com_content&task=view&id=289&Itemid=561
Also suspicious is the fact that Szekely had religious aims in his publication of the "Essene" gospels. He founded an Essene seminary at Rancho La Puerta at Tecate, California, where he expounded on the teachings found in his "discovered" works and lived the lifestyle described therein, and he is recognized as one of the founders of the modern neo-Essene (or perhaps more accurately, pseudo-Essene) movement. His motive in producing the "Essene" gospels is thus to provide a sacred-text basis for his own religious ideas. From what I gather from neo-Essene websites, some neo-Essenes accept his works whereas others reject them as spurious. Of course, there is also the fact that the content of his books show little resemblance to known Essene works from antiquity (aside from the parallels to the Dasmascus Document, which was discovered and published in the 1890s), and there is a curious mixing of Mandaean concepts.
All of this is not to suggest that there isn't any literary or religious worth in the books, Szekely may well have been an original thinker who had some interesting ideas worth reading. But his works should not be assumed to be genuine works from antiquity; they belong to the genre of modern apocrypha such as such well-known exemplars as Joseph Smith's The Book of Mormon, Levi S. Dowling's The Aquarian Gospel, William D. Mahan's Archko Volume, G. J. R. Ouseley's Gospel of the Holy Twelve, Nicolas Notovitch's The Unknown Life of Issa, W. P. Crozier's Letters of Pontius Pilate, H. Spencer Lewis' Mystical Life of Jesus, William S. Sadler's The Urantia Book, Billy Meier's Talmud of Jmmanuel, Glenn Kimball's (?) Kolbrin Bible, etc. Each of these claim to be ancient works, whether revealed spiritually (such as by channelling) or "translated" from ancient documents that have since conveniently "disappeared" or the existence of which cannot be otherwise verified.
