He was told to be a true anti-hero. I have watched AOT and I like him very much. But even then I’ll try my best to give you unbiased thoughts on him and then give you my analysis.
He was a character who flawlessly transitioned between many roles when they were needed. He was a hero when he had to fight against the titans when eldians needed him and when it was for the survival for the sake of Mikasa and others, he eventually got transformed into an antagonist.
The audience could never shake off the feeling that Eren gave them of being right in his beliefs and principles, and it was more than justified of his actions as it was for survival. Hajime isayama is really a genius for building worlds which is more than just exceptional and beyond comparison, and he never fails to point out how worse and how low humanity could stoop to.
When we first met with Eren, he was a young, angry boy who vows to take revenge on the titans after they caused a catastrophe, causing many casualties in which Eren’s mother dies. Which definitely shows off his heroic characters and personality.
Then we could see his anti hero side where he was on neither side. but still upholding his own value but nothing too serious. He’s just doing his job.
Lastly, the moment of proof comes, he upholds his virtue but by upholding them, he kills millions. It was a genocide. and yes, regardless of how one puts it, genocide is bad. And there’s a counter argument for it as they genocided an entire island’s people just because he went over to the other side.
And we can continue with this but he’s just a human who upholded anything that he values. judge for yourself, if he is a hero for being virtuous against hypocrites or is he an anti hero who’s in between or is he a villain for causing a genocide regardless of it’s cause.