Each demo began with your foursome (Cap'n A, Thor, Spidey and Wolverine are the defaults) storming into a heliport to help Nick Fury. Like usual, most helping comes in the form of breaking stuff, though you will push and pull crates and activate switches.
The environments are extremely destructible, to the point where we could easily jump through busted walls for shortcuts. Various mid-bosses pop up, including Scorpion and Bullseye. Talk-trash though they did, the odds are severely against them and they end up beaten down at the hands of our heroes.
Above: Spidey webs the baddies so the rest of the team can run and batter them
After Nick Fury and Black Widow are safe, the demo shifts to a major boss battle - taking on the massive Ymir in his ice domain. We are the ones getting spanked here, as it's apparently quite far into the game - when our characters would be 20-30 levels higher than they are here. One secret debug code later and we're invincible.
This boss fight is very reminiscent of something out of God of War - the huge Ymir unleashes massive attacks, while you battle other minions. Fallen foes drop huge spears, which then must be thrust into Ymir's back. This is not easy and requires either rapid-fire button presses on 360 or controller sweeps with PS3 and Wii.