The text is an authentic old gospel, but not as old as the four canonical gospels. The "Gospel of Judas" makes the case that a) Judas was Jesus’ friend and closest ally; b) Jesus told Judas to betray him in order to move God’s program along and release Jesus from his body; c) therefore, Judas was right to hand Jesus over.
In the text, Jesus tells Judas that he will "exceed all the others." Jesus says Judas will end up sacrificing "the man who clothes me," which probably means the body that clothes Jesus, distinguishing Jesus' spirit from the corrupt body he possesses. (Gnostic sects opposed flesh and matter in favor of the spirit.) The idea is that Jesus wanted Judas to hand him over to those who crucified him, and that by doing so Judas helped God accomplish his divine plan.
Is this positive spin on Judas possible? The devil is in the details. The "Gospel of Judas" doesn't mention that Judas regretted his act and returned the betrayal money, as recorded in Matthew’s gospel. Nor does this Gnostic text say that Judas committing suicide, as described in Acts. If either of these descriptions is true, the ""Gospel of Judas"" version does not make sense.
So which text should we believe, the "Gospel of Judas" or Matthew's gospel and Acts? To answer this question, scholars look at many factors, including the date when a text was written. The four gospels we have in our Bibles, along with the Book of Acts, were written before 100 C.E.
The "Gospel of Judas" was probably written later in the second century; we can tell this because of the developed Gnosticism in it. For example, the text repeatedly mentions aeons and luminaries, typical themes in Gnostic cosmology. (An aeon is a light, a personification of the spirits in the heavens.) We can also connect this gospel to the Gnostic sect of the Cainites, who sought to rehabilitate biblical villains such as Cain, Sodomites, Esau, and Korah. We do know that the "Gospel of Judas" existed before 180 CE, because a church leader named Irenaeus briefly described it in his work Against Heresies (the mention is in Book 1, Chapter 31).
Other things help us realize the "Gospel of Judas" is less historically reliable than the canonical gospels. Jesus' betrayal by Judas is unlikely to be a fabrication of the later church, whatever Gnostic texts might claim. Consider something scholars call the "embarrassment" criterion: if something is an embarrassment for the church, it's unlikely that it was invented. Why would Jesus choose a betrayer as one of his elite twelve? This move casts doubt on Jesus’ judgment, so it's unlikely the canonical gospel writers would have made it up.
So does the discovery of the "Gospel of Judas" do anything for us historically? Well, it does tell us what one Gnostic movement of the second century thought. For example, it retells the creation story this way:
"Then Saklas said to his angels, ‘Let us create a human being after the likeness and after the image.’ They fashioned Adam and his wife Eve, who is called, in the cloud, Zoe."
Here, Eve is given the name Zoe, the Greek word for life. This idea that someone other than the One God is involved in the creation is also common in Gnostic gospels, because God does not create; his underlings, know as demiurges, do.
All of this aids us in understanding second century, but not first century, Christian history. For that one small fragment of historical understanding we can be grateful. The "Gospel of Judas" discovery also corroborates that Irenaeus summarized this gospel accurately, which means we have known about it for 1800 years.
I like new discoveries and the excitement the real ones bring just as much as anyone, but I was hoping for more here. Scholars have hailed the "Gospel of Judas" as evidence of the great diversity in early Christianity, but what the hype obscures is that this text cannot reveal anything about Jesus or the earliest church. As far the original Judas goes, this gospel’s history is about as dilapidated as the codex on which it is written.