In another discussion, I stumbled across an interesting theory about Jarvis vs JARVIS.
Tony grew up with an abusive, distant, mostly-not-there alcoholic father (Howard Stark). That would mean that for Tony, the butler Jarvis would have been more or less a substitute father. Thus when he created an AI, he patterned it after Jarvis. So in effect, JARVIS is the father-companion Tony wishes he had. That might explain why JARVIS gets away with criticizing Tony in ways that he probably wouldn't accept from others.
Anyway, they really screwed up Ultron.
Ultron was created, and within seconds decided to destroy all of humanity. The audience is never given enough time to emotionally process what's going on. Ultron never developed a relationship with his creator, so the audience gets no sense of betrayal when Ultron goes rogue within seconds of being created. More importantly, we don't get to feel the tragedy of an AI created with a prime directive that is actually impossible to fulfill. Instead it's just BANG Ultron exists BANG "I'mna kill everyone. Because."