In Buffy did anyone else notice Angel's personality change? Or when about it happened?

I'm re watching the first season of buffy (currently the Pilot) and Angel has this certain attitude about him, hes sarcastic, and I don't exactly know how to describe it but it was a great attitude. I know at some point he loses it and becomes broody, But i can't remember when. I'm thinking he came back in season 2 like that but I'm not sure?