Kaneki in the manga is a character while in S2 of the anime he isn’t. After the big moment he builds a team and constantly trains to take down this organization. We know exactly what he’s thinking and how everything has effected him.

The anime Changes the story in S2 by having Kaneki join this organization that he was fighting. Then he disappears for most of the season and most of his scenes have him act like a emotionless mute. So whenever he has a big fight and goes crazy there’s nothing leading up to that moment. The last couple episodes try to do some stuff with his character but it doesn’t work very well.

I don’t want to put all the blame on Studio Pierrot since they were told to make S2 right after S1 with barely any time. There is also a lot of misinformation that the studio threw out Ishida’s drafts for S2 (which fixes a lot of stuff btw) but it seems like it happened because of time. The director explains most of this in his AMA