We see this world through the eyes of Winston Smith who judges the totalitarian society that he lives in. Because of this we easily adopt the mood he has for the government and society in which he lives.
In part 1, Winston struggles with the society and curiously questions on the inside the purposes and motives of the Party. He has this longing to rebel, but never truly acts on it in the open, only in the privacy of his mind. Words I would use to describe the tone in this part include: inquisitive, curious, contentious, questioning, and tolerant.
In part 2, Winston and Julia begin a risky relationship and Winston further believes in possible resistance to the Party. Thus, this tone could be considered more daring, risky, unashamed, motivated, and willing.