I've been wanting to do an expose of sorts on the Gospel of Judas for some time now, but since other brilliant minds have already written refutations of the claims of the "false gospel," I'll provide here the most relevant links to the story I can muster, with synopses of their contents, and leave my readers to hopefully research them for their own benefit.  Then I'll write a brief conclusion.  First, the primary sources:

What It Is. 

• An ancient story about Jesus' secret teachings, especially those which he taught to Judas Iscariot.  See the complete English translation of the text here (pdf) from National Geographic.
  
• According to a news source, the National Geographic Society purchased all rights to publicize the Gospel of Judas manuscript, along with some other ancient works contained in the same codex, for $1,000,000.  As a result, the Society was able to mount a phenomenal (secret, like the gospel itself) marketing campaign, beginning in 2004, and resulting in the nearly simultaneous publishing of a press release, exclusive photographs, a National Geographic magazine article, at least two books, and a television documentary.  Strangely enough, the Society, perhaps in the excitement of its exclusive press release rights, seems to suggest that this "lost" gospel will seriously challenge traditional Christian beliefs.
  
• The Judas gospel consists of 26 pages, badly deteriorated and partially fragmented, written in Coptic script.  It is part of a codex--an ancient book of bound pages--that was apparently discovered in the 1970's and endured a lengthy and shady series of trades from dealer to dealer before being bought by the Society.  You can take a close-up look at the pages yourself with NG's "Manuscript Magnifier."  The magnifier features pages of the gospel that contain the most controversial statements, such as Jesus' alleged words to Judas: "[...] you will exceed all of them. For you will sacrifice the man that clothes me.”  Taken in light of Gnostic interpretation, which views the body ("the man that clothes me") as evil, this statement is taken to mean Jesus was inviting Judas to deliver him over to death.
  

What People Are Saying About It. 

• The New York Times published a story (reprinted in the International Herald Tribune) questioning the historical claims of the Gospel of Judas.  It quoted Professor Ben Witherington III of Asbury Theological Seminary saying, "The manuscript tells us nothing about the historical Jesus or the historical Judas."
• Clinton E. Arnold, Professor and Chairman of the Department of New Testament at Biola University, has posted a question and answer page about the Gospel of Judas discovery.  It is very informative about the manuscript, the Gnosticism behind the false gospel, and the implications for Christians.
• The Lincoln Journal Star has an insightful story about early Gnosticism, and the Judas gospel's presentation of God.
• One of the best rebuttals of National Geographic's sensationalized press release was written by David Kopel at The Volokh Conspiracy.  A flat-out good read.
• Many other sources have published a correct view of the Gospel of Judas, including Christianity Today, The Salvation Army's War Cry magazine, Baptist Press News, and Creation-Evolution Headlines (here and here), which first published many of the helpful links included in this post.
• Tertullian.org has compiled a chronological list of academic reports related to the Gospel of Judas manuscript.  I leave it to my readers to discern the accuracy of the information contained there.

The Run-Down

The Gospel of Judas is a purely Gnostic work.  It exists in only one known extant manuscript (and that badly damaged) and was probably written around 180 A.D. when it was condemned by Christian church father Irenaeus of Lyons as heretical.  In contrast, there are as many as 25,000 extant manuscripts or portions of manuscripts of New Testament books in Greek (5,686), Latin Vulgate (10,000 or more), and other languages of the period. The only other Greek work that comes close to this level of authentication is Homer's Illiad, which exists in 643 manuscripts. (See Josh McDowell's The New Evidence That Demands a Verdict.)  The canonical gospels (Mathew, Mark, Luke, John) were written while eyewitnesses of Jesus' earthly ministry were still living.  These gospels were circulated widely among Christians because they were known for their accuracy.  As a result of their popular acceptance, they were included in the New Testament canon, and later works, such as the Gospel of Judas (written around 180 A.D.) and the Gospel of Thomas were rejected as unhistorical, fictional, and heretical.

The short Gospel of Judas reflects the belief system of Gnosticism, which deviated from Biblical teaching and was condemned by the Early Church.  Gnostics taught that the body and all material things were evil, and that salvation could only be achieved through the acquiring of secret spiritual knowledge.  It is this sort of knowledge that the Gospel of Judas advertises in its opening line: "The secret account of the revelation that Jesus spoke in conversation with Judas Iscariot during a week three days before he celebrated Passover."  The gospel goes on to portray Judas Iscariot as the only disciple who truly understood the nature of Christ.  In this gospel, Jesus is quoted as sharing with Judas his secret knowledge of creation, the angels, and the afterlife--there is no teaching about practical living, as the Christian canonical gospels record in length.  Furthermore, the Gospel of Judas calls into question the nature of Christ, and of humanity's ability to know him: 

One day he was with his disciples in Judea, and he found them gathered together and seated in pious observance. When he [approached] his disciples, [34] gathered together and seated and offering a prayer of thanksgiving over the bread, [he] laughed.
The disciples said to [him], “Master, why are you laughing at [our] prayer of thanksgiving? We have done what is right.”
He answered and said to them, “I am not laughing at you. <You> are not doing this because of your own will but because it is through this that your god [will be] praised.”
They said, “Master, you are […] the son of our god.”
Jesus said to them, “How do you know me? Truly [I] say to you, no generation of the people that are among you will know me.”

The New Testament lays out a clear concept of the nature of Christ--he was both God and man--and presents its doctrine in such a way as to make it available and knowable by all, not just to a secret group.  Anyone who disbelieved either Jesus' humanity or his deity could not be saved.  Early Christians also saw the New Testament, including the life and teachings of Jesus Christ, as a compatible fulfillment of the Old Testament, preserved in Judaism.  However, many Gnostics disliked the concept of God portrayed in the Old Testament, and actually venerated Biblical characters like Cain, who murdered his brother after God spurned Cain's sacrifice, and the residents of Sodom, homosexual men who attempted to rape two angelic visitors.  They also held loose views of abortion, infanticide, and war--a consequence of their teaching in the evil nature of the body.  In being crucified, they believed Jesus was achieving a greater union with God, by casting off his body of flesh.  This implies that Jesus was not fully God during his fleshly life, and the result of this assumption is that Judas was doing Christ an eternal favor by betraying him to his murderers.

Enemies of the flesh, of God, Christ, the Bible and historic Christianity, its no wonder the Gnostics made a hero of Judas.