Okay I wrote a bit about it in another post, so I'll copy it here.

I felt Eren's character regressed in the last chapter. Prior to 139, he played the role of a uncompromising, but guilt-ridden realist. He condemned Hange and the Azumabito for being overly idealistic and trying to play both sides, without offering a reliable solution for long-term peace. He abandoned them and used the Rumbling to kill all his enemies for peace. But he wasn't some cold, inhumane killer; in 131, you could see that he was still the same emotional young man just trying to protect his people from the outside world, but even being guilt-ridden to death by all the murder he was causing, he wouldn't stop because he saw it as the only realistic way to save his friends. This is some beautiful characterization right here. But in 139, he's suddenly okay with risking leaving a huge portion of his enemies alive to retaliate one day. The character development is dropped and in the end, Eren feels like a hypocrite and no different from Hange/Azumabito in his idealism.

Eren actually never stopped showing real human emotions. Chad Eren was never emotionless, he only tried to hide his emotions from his friends. In reality he was being torn apart by guilt, but wouldn't stop murdering because he felt the only reliably safe future was with all his enemies dead.