Everything, it mischaracterizes him, it's too tame, and his split personality wasn't even something I thought about until close to the end of his route then added some vague stuff in between to hint at it.
Don't even get me started on the Headmaster's writing.
It also feels very unfair that Aiden's route literally became a unit of measurement for other routes "Tate's route is as long as 3 Aiden routes!"