When Tony Stark and Bruce Banner try to jump-start a dormant peacekeeping program called Ultron, things go horribly wrong and it's up to Earth's mightiest heroes to stop the villainous Ultron from enacting his terrible plan.
Avengers (or Avengers Assemble) was fun, exciting and brought the heroes together perfectly. This pile of whatever was slow, meandering and not that great at all (unless you're comparing it to a DCU film that is). This was filler.