Oh, and Iron Man's new armor and Captain America's uniform but OH MY GOD IT'S ULTRON AND HIS ROBOT MINIONS. This is obviously the cover for Entertainment Weekly's Comic-Con issue — which has the first Avengers: Age of Ultron synopsis, too.
For better or worse (trust us, it's worse), his Tony Stark has devised a plan that won't require him to put on the Iron Man suit anymore, and should allow Captain America, Thor, Black Widow, Hawkeye, and the Hulk to get some much needed R&R as well. His solution is Ultron, self-aware, self-teaching, artificial intelligence designed to help assess threats, and direct Stark's Iron Legion of drones to battle evildoers instead.
Ultron, obviously, decides the easiest way to save humanity is to destroy all those problematic human beings.
The hard part about battling Ultron, as the cover image suggests, is that he's not just a robot—he's a program, capable of uploading himself and disappearing not into the clouds but the Cloud. And he has a bad habit of rebuilding himself into stronger and more fearsome physical forms.
The EW article has details from director Joss Whedon, Robert Downey Jr., and more, so definitely go check it here.