3PO in SW is a lot different than in the sequels. Much more sci-fi/robotic and more monotone. Later he became more approachable and human.
That’s an interesting point. Much of his emotion seems to come from past experiences, which would work for a droid. Like “I’ve forgotten how much I hate space travel” would come from having known it hasn’t been pleasant in the past.
However, hanging around humans so much would likely result in him potentially becoming more human, if that’s the way he was programmed. He still keeps a bit of a robotic nature though (In Empire he says Luke is clever “for a human being, that is”) and he really mainly cares about himself(see the whole third act of Empire, when he’s complaining about being on backwards as Han is being frozen alive)