Disclaimer, I have not read his books.
But I readthis article, and if these descriptions of what he writes in his books and claims to be autobiographical are accurate, he does not come across as “all there” to me. According to the author:
He describes aliens as having a sort of parasitical telepathy with us, and that some “hate us with a passion so great that it would be considered psychotic if it was displayed by a human being” and that they are essentially what is keeping us trapped here on earth instead of being “cosmic beings” whatever that’s supposed to be.
He is inconsistent in his description of what the aliens are and what their purpose is. At times he describes them as physical beings trying to revive their own species using humans, and others as non-physical beings trying to bring humans to a higher plane of existence.
He described, in different books, encounters with aliens as being visited by demons and as angels. Meaning, he described the exact same events as if he had changed his mind as to what they were.
He claims to have an implant by the aliens, and to have powers like telepathy and time travel and interdimensional travel.
He claims to have recovered memories of being abused by the Government in a secret mind-control experiment as a child: “I strongly suspect that the United States has for years been experimenting on children, among other things subjecting them to extreme trauma in order to split their personalities and create secondary personalities who can be accessed by controllers and used as agents, but without knowledge of the first personality.” And this is why the aliens came to him, instead of other people.
Then there’s this bit, which I’ll just quote 'cause it’s kinda hard to do justice to:
“If Strieber continues to be unable to decide whether his nocturnal visitors are angels or demons, it’s hardly surprising if he feels profoundly ambivalent about his task as bellwether for the alien paradigm. In his early books, he suggested that, since the beings appeared to emerge from a nonphysical realm, their reality, for us, might depend on our belief in them. In 2012, Strieber stated this unequivocally: the “aliens” can only enter our realm once they have assumed sufficient “solidity” via our collective belief, and to emerge from the dark well of the collective psyche, they require a foothold in our conscious minds. Strieber even stated that the government cover-up (which he once railed so bitterly against) was a means to protect the world from that emergence. The day public awareness of the alien presence reaches consensus, then, alien “invasion” will not be far behind. Yet for years Strieber has been denouncing the secrecy and denial shrouding the visitors as the great evil of our times. Although he has admitted that their undisclosed presence among us would be catastrophic, he has mostly argued for full disclosure. At times he has even suggested that awareness of the beings is the only thing that will protect us from them.”
And keep in mind, all of this is from an article that is very much trying to convince skeptics to take Streiber seriously.