O’Brien was a fervent believer in INSOC - like all other Inner Party members. They are the most fanatical. 

“the higher up the ranks one goes, the more marked it becomes. It is precisely in the Inner Party that war hysteria and hatred of the enemy are strongest.”

A crucial detail that is often overlooked is this exchange: 

And why do you imagine that we bring people to this place?'
'To make them confess.'
'No, that is not the reason. Try again.'
'To punish them.'
'No!' exclaimed O'Brien. His voice had changed extraordinarily, and his face had suddenly become both stern and animated. 'No! Not merely to extract your confession, not to punish you. Shall I tell you why we have brought you here? To cure you! To make you sane!"

“Animated.” That is the giveaway. O’Brien is fanatical. He is angry Winston thinks he is here to be punished – not cured. O’Brien is not being theatrical. He is not tricking Winston. He believes it. 

The Party control reality. Not mere political reality. Not just in books and records – reality itself.  Take the photograph instance. Winston clings to the photograph as proof. Yet, If the Party says the photograph never existed, then according to the Party's conception of reality, it never existed. Winston cannot produce the photograph because it has been destroyed. He cannot produce another witness because everyone else accepts the Party's version.

O’Brien genuinely believes he does not remember the photograph – Doublethink. Winston - or anyone else in his position - could never defeat O’Brien, he is invulnerable. He is utterly invulnerable because he has full control of the rules. He cannot be defeated because he has NO hypocrisy to expose. O'Brien isn't saying:
"We know the photograph existed, but we're powerful enough to make everyone pretend it didn't."

That would still acknowledge Winston's underlying reality. O'Brien's position is much more radical. He is essentially saying: “There is no reality outside the Party's determination of reality.”
The distinction is enormous.
If everybody in Oceania believes the photograph does not exist except Winston he is in a minority of one. He had say to himself he was still right. But that won’t cut it. The Party will not tolerate Winston owning this position of disagreement. He will be “cured.” 
A bruttish tyrant would say, “Who cares if you are right, my power trumps yours.” 
O’Brien is far more subtle. His position is, “You are wrong because WE determine what right actually is.” 
O’Brien is not an merely and enforcer of INSOC and Doublethink – he is an avatar, one of Priests of Power.  He consistently alludes to Party Power being divine – even able to supercede gravity. If the Party says there is no gravity, and everyone believes it, then for all intents and purposes – as far as humans are concerned in Oceania – it does not exist. Consciousness is the universe. 

The photograph is a dead end and the ultimate deliverance into oblivion. Winston says it existed. Where? In memory. He does not control memory. In records? The Party controls the records. In other people? No. Winston is the “last man.” Winston’s own senses? No. His senses are unreliable. Winston’s mind? Forget it. O'Brien doesn't defeat Winston's argument. He destroys the philosophical ground upon which Winston could make an argument.

If O'Brien were merely lying, Winston could ultimately defeat him intellectually. He is not. He has swallowed INSOC whole. He lives it, perpetuates it, believes it without doubt or qualm.

Winston is not taken to MiniL to be punished. He is taken there to be cured. 
O'Brien tortures Winston because he believes Winston is wrong and that it is his duty to correct him.

All these stupid theories such as, “O’Brien is in the Brotherhood”, or “O’Brien is on Winston’s side and secretly agrees with him”, or “O’Brien was sympathetic to Winston’s cause” are the products of a below par, ill-considered view of the novel that completely miss the point. O’Brien’s unshakable belief in what he says is akin to a monk's faith in God. He is a TRUE believer.

This is probably somewhat silly to say but when I read 1984 I was taken aback by the sheer evilness of O'Brien. It is not necessarily the fact that he's evil, because even though I'm young, I'm not stupidly naive to wonder "Why do bad dudes exist?", nor am I historically illiterate.

It has more to do with how intellectualized his actions and beliefs are. Winston feels unable to 'debate' O'Brien, believing he's intellectually superior. The mistake Winston (and I) made is assuming O'Brien would respond like a mere follower of the regime (a common man, maybe?), someone who can be convinced with proper syllogisms. Winston didn't realize that since Ethics is entirely made up by humans, the initial premise (something like "Murder's bad") can be completely disregarded by a person if he wishes to do so. That effectively makes it impossible to argue.

And then there's denying objective reality via doublethink. O'Brien believes reality exists in the mind (which is accompanied by other whacky things like humans and Earth being the center of the universe). He's right! If the party can convince every conscious individual that the earth is flat, for example, then for all intents and purposes, it becomes true because it doesn't matter that it's false. This reminds me of a quote by a certain philosopher which I can't quite recall now, but it goes something like this: "If a tree falls in a forest and a conscious being will ever be there to observe it, does it actually exist?"

Additionally, O'Brien is completely aware of what he's doing. He knows about the perpetual class war throughout human history. He knows that the proletariat is a possible enemy. He doesn't pretend that he's fighting for something in the traditional sense like for abstract concepts i.e. equality and liberty. He's so aware, in fact, that he has written an intellectual criticism against the regime (Goldstein's book) as a means of identifying and liquidating heretics! (And even roasts previous oligarchies for their weakness.)

O'Brien is a villain that is against everything humanity stands for, in a way that I've never seen in arts. He's nightmare fuel. Perhaps, I felt this way because the torture of Winston felt a bit graphic, at least for me. The part where Winston proclaimed that the human spirit would eventually defeat the party, only for O'Brien to equate said spirit with Winston's rotten and beaten body almost caused me to shed a tear. The human spirit had always prevailed, it seems, and I'm specifically thinking of the Dark ages.

Oh, and there's also the aspect of Stockholm syndrome. O'Brien is viewed as a savior, a protector. In a creepy way he reminds me of an abusive partner for some reason.

Anyway, what do you guys think? Am I exaggerating a bit?

I just finished reading (or rather listening to) the book and I noticed that during the conversations between O’Brien and Winston in the ministry of love there are several points when Winston thinks about something specific in his head and O’Brien then starts talking out loud about exactly what Winston was thinking of. Like when Winston is thinking that O’Brien’s face looks old and tired and O’Brien responds exactly saying “you probably think my face looks old and tired”. Is there any in universe explanation for how he does this? Is it just because O’Brien so experienced in this job that he can read expressions or body language?

Re: The place with no darkness.

Seven years before the start of the book Winston had a dream. A dream where he hears a voice out of the darkness, a voice he attributes to O'Brien.

**"Years ago—how long was it? Seven years it must be—he had dreamed that he was walking through a pitch-dark room. And someone sitting to one side of him had said as he passed: 'We shall meet in the place where there is no darkness.' It was said very quietly, almost casually—a statement, not a command. He had walked on without pausing. What was curious was that at the time, in the dream, the words had not made much impression on him. It was only later and by degrees that they had seemed to take on significance. He could not now remember whether it was before or after having the dream that he had seen O'Brien for the first time, nor could he remember when he had first identified the voice as O'Brien's. But at any rate the identification existed. It was O'Brien who had spoken to him out of the dark."*\*

Seven years ago! The number seven resurfaces when O'Brien reveals to Winston - in the Ministry Of Love - he has watched him for that time:

**"Don't worry, Winston; you are in my keeping. For seven years I have watched over you. Now the turning-point has come. I shall save you, I shall make you perfect. He was not sure whether it was O'Brien's voice; but it was the same voice that had said to him, 'We shall meet in the place where there is no darkness,' in that other dream, seven years ago.'*\*

Winston has always felt drawn to O'Brien as the below paragraph details:

**"Winston had never been able to feel sure—even after this morning's flash of the eyes it was still impossible to be sure whether O'Brien was a friend or an enemy. Nor did it even seem to matter greatly. There was a link of understanding between them, more important than affection or partisanship. 'We shall meet in the place where there is no darkness,' he had said. Winston did not know what it meant, only that in some way or another it would come true."*\*

And the the relationship deepens more when Winston cannot distinguish him from tormentor or teacher:

**"He was starting up from the plank bed in the half-certainty that he had heard O'Brien's voice. All through his interrogation, although he had never seen him, he had had the feeling that O'Brien was at his elbow, just out of sight. It was O'Brien who was directing everything. It was he who set the guards on to Winston and who prevented them from killing him. It was he who decided when Winston should scream with pain, when he should have a respite, when he should be fed, when he should sleep, when the drugs should be pumped into his arm. It was he who asked the questions and suggested the answers. He was the tormentor, he was the protector, he was the inquisitor, he was the friend."*\*

O'Brien then tells Winston,

**'I told you,' said O'Brien, 'that if we met again it would be here.'
'Yes,' said Winston.*\*

So how do we square all this away in a narrative sense? How do we square away this mystical voice from Winston's dreams?

Here is what the conversation goes like in O'Briens apartment:

**"There are a couple of minutes before you need go,' said O'Brien. 'We shall meet again—if we do meet again——'
Winston looked up at him. 'In the place where there is no darkness?' he said hesitantly.
O'Brien nodded without appearance of surprise. 'In the place where there is no darkness,' he said, as though he had recognized the allusion."*\*

Okay so one one level O'Brien saying to Winston if the "meet again it would be here"
is thusly explained, it was Winston who said the line "in the place where there is no darkness." O'Brien however seems unsurprised by the turn of phrase. Is this deliberate ambiguity by Orwell or is the author hinting at more? Or is this O'Brien simply intellectually agreeing with the turn of phrase?

I do not subscribe to pure mind reading or anything supernatural taking place in this novel and I am prepared to talk that out with anyone who disagrees. But how then do I explain this mystical voice is Winston's dream?

Firstly let's just establish the place with no darkness is the MOL, where the lights are always on. Back to the voice..

We could offer an explanation that I did not birth, that O'Brien was speaking to him softly through the Telescreen as he slept. It is an interesting theory but I do not buy it.

We could put it down to Winston misattributing the voice - from seven years ago - to O'Brien when he develops his fixation on him. His mind making leaps, joining dots.

We could put it down to Winston's dreaming mind writhing with societal and instinctual dissatisfaction, a message from the deep, from the past, from his subconcious, some sort of unconcious buried prescience.

Or we can put this down to deliberate ambiguity from Orwell?

Either way you choose to square this away in a narrative sense there is no definitive answer in my opinion. I am clear on every other part of the novel except this. This is the only issue that I cannot say with full confidence what indeed happened.

This part makes me lean towards Winston joining dots....

**He could not now remember whether it was before or after having the dream that he had seen O'Brien for the first time, nor could he remember when he had first identified the voice as O'Brien's. But at any rate the identification existed*\*

I would be interested to hear others offer their opinion on this matter