Originally Posted by Jordacar
Ultron is an iconic villain, but a pain-in-the-ass to introduce into a film.
The reason is that like Venom, Ultron's story was told in a series format, in many comic issues with many phases in his development, rather than a 2-hour film with a clear beginning, middle and end.
Well the way to do Ultron is not to introduce him only within a 2 hour film. Introduce him and Pym in other MCU movies, so that you see a little bit of development throughout these pictures, even if it is really small. At least have him there in the background, like how SLJ had these cameos. Then by the time it gets to a proper Ultron-centred movie, it doesn't look like he was just plucked out of a hat. I would say even introducing him in Phase 2 movies so that he can be ready for Avengers 3 in Phase 3.
Marvel shouldn't have the same problem as Venom in Spider-Man 3, because they've got several films in which to introduce a character and plant seeds for development.