I just saw it again last night, and focused on Nebula. The first time I saw the movie, I was a little disappointed with her, because Karen Gillan had described her as unhinged and a psychopath. This time I realized she was very unhinged but in weird ways. She constantly yells and is always foaming at the mouth. Her walk tries way too hard to be a "commander" walk. (Towards the end of the movie, when the Dark Aster is just starting to be attacked, and when she's ordering sakarrans about and then leaves the main room that Ronan is in, she does this priceless funny walk out of the room in the corner of the screen) These both probably tie into her sort of inferiority complex about being her father's second favorite. She thinks she's terrifying, and she definitely is, she thinks she the Thanos type terror when really she's more like Ronan with a healthy dose of Harley Quinn. That isn't to say that she isn't violent and psychopathic, but she does it in a way that gives the characters a lot of layers.