Honestly... the only Ultron story I've read was the one in Runaways.
Watching him on EMH doesn't give me any ideas either. You could always do him like a typical AI villain wanting to upgrade humanity or some such, but I wasn't clear how much of that had actually been used with him in the past.
Thinking about that, he could actually create the Life Model Decoys without it being a joke. Going further, he could be as powerful as he is (Adamantium Shell, Encephalo-Beams or whatever) because he feels he can more efficiently defend the planet than the Avengers. That'd be a nice twist for a robot villain.