@miyako19 He was called the fool of Owari because he generally disrespected tradition and propriety (often played with townsfolk dressed as a commoner, spoke slang, disrespected the court) ultimately culminating to when he disrespected his father's funeral, which was one of the reasons why him being lord of Owari was so contested. He eventually started acting his station and minding his image, but never actually respected tradition, which is why he was so willing to burn down temples when they went against him like the warrior monks of Mt. Hiei. I'm not going to say he wasn't ruthless, but he definitely drew a clear line between his retainers and his subjects (the people). He would be curt with his retainers and more open and warm to his subjects. AFAIK Mitsuhide's mother died because he used her as a hostage to have a castle open during a siege. I don't know if it was ever stated that Nobunaga forced him to.
His reluctance to follow traditions made people villainize him more than he should have been, especially in the Edo period while Tokugawa and his descendants were trying to secure their place.