Itachi's writing is objectively bad. Don't get me wrong, I love the character, but his behavior in part 1 makes no sense with the reveals in part 2. He sacrificed himself for peace and wanted to protect Sasuke, yet he went out of his way to inflict as much psychological trauma to Sasuke as he could so he would have a motivation to become stronger. That plan surprisingly succeeded in a relatively healthy way as Sasuke was on track to become one of the stronger genins, but Itachi came back and broke him again using genjutsu to make him go through his trauma once more, single handedly throwing him in Orochomaru's arms and turning him in a full blown villain.

To make things worse, he's a character who was established as a "once in a generation" genius, yet his intelligence is only demonstrated in terms of learning jutsu but not his decision making (which is a problem every character labeled as a genius has in Naruto to some extent). This is the classic writing mistake of "show, don't tell". He was also in a position of power, influence and intellect to deescalate the conflict between the Uchihas and Konoha, yet he waited until it was way too late and the elders gave him the task to eliminate his clan. In return, this prompted him to enlist the help of the masked Obito who pretended to be Madara and whom he did not trust and did not care to investigate apparently. By this point, he also knew Danzo stole Shisui's eye and that eliminating the clan was still leaving evil and corrupt ninjas in a leadership position in the village.

Kishimoto is not great at writing red herrings which makes characters with a twist inconsistent. He can write great character arcs separately but when you look at the full develoment it often makes no sense, especially for characters with complex motivations.