I went to this movie cold as I didn't have any intention of going to the cinema to watch this....
Ultron significantly better than the first. The first was an adequate movie which had a monotone pace. Was predictable, awkward, had generally uninteresting action, poor motivations for inter-team conflict, too much Stark also what the point of Hawkeye?.
Ultron is has generally natural characters, most of the action is pretty good although for some reason they decided to ruin chunks of it with shakey cam. Had a good varying pace that let you breath a little, although it is slightly overly aggressive with the editing which was done to keep the length down as it is a long movie that might have been 2 movies, so between the two evils, they chose the right one. We still have a Hawkeye problem where he is still an outsider, but he doesn't bring that to the group and it more for personal brooding.
Stark is something of an imbecile where he once again doesn't think about the consquences of his actions, even from one moment to the next. He never faces up to them ever. Sure he "Fixes" things, but he never takes personal responsibility.
Overall Joss has learned from quite a few of his mistakes and has made a better movie. Good for him and I would wish other directors would do the same but that's not going to happen, if anything else most directors get worse.