Physically, Winston is aghast when he sees himself in the mirror for the first time since being imprisoned. He has lost his hair and an immense amount of weight, and his skin has a grey pallor (suggesting not only illness but also a lack of light exposure). Whenever I read this section of 1984, I picture a Holocaust victim and wonder if Orwell perhaps had the same image in mind.
Emotionally, Winston has lost all control of his emotions. At times he loves and almost worships O'Brien, and then he switches to being dreadfully afraid of him. He thinks that he loves Julia, and his "loyalty" to her is the one thing that bouys him with a small amount of hope. Even that "constant" emotion is destroyed when O'Brien orders Winston to Room 101. After he is completely broken near the novel's end and sitting in the Chestnut Bar, the final and only emotion that he is able to summon with tears is his "love" for Big Brother.
Mentally, Winston lives in a dreary, surreal world after he is released. He spends most of his time drunk so that no real thinking can occur. Once so mentally accute that he is assigned to a meticulous job at the Ministry of Truth, Winston becomes so dull that his new job does not require that he do anything.
In the end, the Party is successful in destroying Winston physically, emotionally, and mentally--in essence, preparing him for death.