Gnosticism can be hard to pin down to a specific set of beliefs. It tends to be "syncretic" (merging the beliefs of multiple groups). It also is highly dualistic, expressing a sort of battle between the material and immaterial.
The "Gospel" of Judas is believed to be a Gnostic work. It is certainly typical of the beliefs ascribed to Gnosticism. That is, the material world is evil, and the immaterial (or spirit) is good. There is also (usually) an emphasis on the obtaining of knowledge as necessary for salvation (especially secret knowledge). The roots of many modern cults and "new age" fads are in Gnosticism.
The root ideas of Gnosticism were around during the writing of the Bible (and remain today). In 1 John 4:3b, John says "And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God". This is because some would say that Jesus, being God and good, cannot be flesh (which they assume is evil).
Jesus is 100% God, 100% man.