The following is a spoiler filled summary from yours truly, who attended the panel
First it starts out at a party. Tony tries to lift Mjolnir and fails. Then Bruce does and also fails and Maria Hill jumps thinking he'll hulk out. Then Tony tries with his armored arm and fails. Then he tries with Rhodey and fails. Then Steve tries and barely moves it. Then THOR makes a joke about not being worthy and picks it up and flips it. Then Ultron crashes the party with his bots. Thennnn it shows the hulkbuster armor and bruce in the snow. Then it shows widow and hulk's hands touching in a romantic way. At the end it showed steve's shield completely destroyed and him possibly dead and battered. It also showed loki's scepter at one point.