I didnt really like it that much. The Ultron thing was done so quick. They build him in five minutes, turns evil in 30 seconds, introduces himself, then everyone knows what's up and what he's about.
The plot was just by the numbers, almost a repeat of the first film with less humour. Watching impossible men in an impossible world get thrown around, where flesh is stronger than concrete, and you can barely tell what is happening, is becoming less interesting to me. And the whole fight the robot/chitauri army thing is really dull(at least the first avengers had those giant leviathan things).
I much prefer something like the Winter Soldier, felt much more tension in that, that thing's were at stake that Captain America could fail. The action was much more down to earth, the lift scene and highway scene are works of art.