What didn't you like? AOU was awesome. Much better than the original. Better action, better story and better dialogue. You have to realise Whedon cut an 1hr out because the studio and cinemas said that 2 1/2hours is long enough. There was a lot in there and great subtleties. I've seen it 3 times and recommend a second viewing.
Ultron is stripped of the personality from the comics. The suddenly leap "kill all humans" is just that, too sudden. We see the same rehashed hero inner conflict from Avengers, Thor 2 and Ironman 3. Yes Tony has issues, we get it. We see the same villain and massive army concept from Avengers. The same central villain followed by incompetent or inconsequential lackeys which only foreshadows a grand villain which has the same flawed lackey's as his puppets. I would of liked to see the rise of the standard rival villain group. I do not think this will happen in the Avenger's universe with it's the branching single hero focused setup movies do nothing to suggest anything but a grand villain vs "us" showdown. Maybe the X-Men remakes will keep the concept of group vs group going.
I did enjoy the movie. I just have issues with the writing and direction the series as a grand story arc.