There were many flavours of gnosticism, but they all – at least those derived from Judaism or Christianity – had some things in common.
A particular creation myth, and obsession with the first generations of people.
A conviction that redemption is found not through atonement or forgiveness, but through ignorance. Only through complete lack of knowledge and critical thinking could you make that sudden and complete realisation of the gnosis, the vast and complex conspiracy which explained how the world really worked.
A conviction that this world is evil.
Evolution is a fake, and creationism the truth; Obama is a fake president, and not the real one; the Founding Fathers were fakes, not the servants of God who really created the Constitution; there is a vast conspiracy of evil in the world which can be called communism: a Manichean battle being waged against the forces of public education, public health and public debt, science, and gun-deniers and corrupted religions.
Gnosticism seems to have erupted again amongst the Tea Party and in the Republican parts of the USA.