For the sake of transparency I am firstly going to clarify that I am not a Historian nor studying it as a subject. Instead I am studying Religion as a subject and parts of that touches upon religious history. I have had an interest in Gnosticism for a while and so have read up on it.

As a religious text answering how 'reliable' it is is somewhat a vague question. The answer ultimately depends on what you mean and from what perspective you are approaching the text.

If you mean, was the text looked at religiously, then yes it was. Sethianism was a Gnostic group in early Christian history. From what we know of them they held the 'Apocalypse of Adam' to be a holy book, along with other books such as 'The Gospel of Judas', 'The Secret Book of John' and the 'Holy Book of the Great Invisible Spirit' among others. Generally Gnostic religions claimed that they had access to special revealed information that other Christians were not privy to.

As you may have read as well the 'Apocalypse of Adam' goes on further to claim a radically different understanding of the world than the Christian one. Of central importance is the claim of there being a God above God and that the God who created our universe was in fact 'ignorant' of the true nature of themselves and the world or in other words 'evil.' It also radically changes the way the events of Eden are interpreted. All of these are what Sethians truly believed from our knowledge.

If you mean, is the text religiously accurate from a Christian perspective, then no. Early Christians rejected the Gnostic sects and considered them heretical. Part of the Nicene Meeting and resulting Creed was rejecting these 'heretical texts and beliefs' as the Church considered them. To my current knowledge there exists no denomination that considers the Gnostic texts as accurate.

(To address a question some people may have, Gnosticism as a definition is a bit murky. It seems the term was applied to any group with a radically different understanding of the universe from Christianity that didn't already fit under another term. It seems that the groups or individuals actual beliefs weren't being matched with some checklist of criteria in order to be considered Gnostic. In fact there seems to be some debate over how related these groups even were to each other, especially some that only emerged later in history and seemingly had no connection to their historic peers.)

And finally if you mean, what do all the other religions/what does X religion think about the text, then I must admit we have reached the limit of my knowledge. Ultimately though I think it would be useful to consider how a religion perceives Christianity first as that will probably give insight into how it would perceive a Sethian text then.

As for how historically accurate it is I belief that ultimately comes down to how much weight and how literal you wish to read any religious text. In the end this does come down to your own faith but academically it's narrative would be held as wildly inaccurate to say the least.

For this answer I am using the books 'Studies in gnosticism and in the philosophy of religion' by Gerald Hanratty and 'The gnostic Gospels of Jesus: the definitive collection of mystical gospels and secret books about Jesus of Nazareth' by Marvin Meyer.