Talk about tough. In replacing Raven Software on the Ultimate Alliance series, developer Vicarious Visions has a huge challenge. The first game sold millions of copies, had 25 playable heroes, and spanned all corners of the Marvel Comics universe. How do you top a game that had everything?

Well, they’re starting with a few key elements: a better story, enhanced visuals, and an exciting new co-op mechanic.

The story won't be strictly Marvel canon, Vicarious says. They have permission to veer a bit from official mythology.

MUA 2 opens with the events of Secret War, the 2004 comic-book miniseries in which Nick Fury sends a small group of heroes into Latveria to quell a terrorist plot. Though Activision wouldn’t officially confirm this, it’s clear from the level we observed that the game’s story also covers at least part of the recent Civil War crossover, which pits hero against hero when some resist a new law compelling superhumans to register with the U.S. government. Both tales embody serious post-9/11 themes of liberty versus security — giving this sequel a narrative weight that’s way beyond the skeletal story in the first Ultimate Alliance.

Of MUA 2's 24 playable characters, the others announced so far are Captain America, Green Goblin, Human Torch, Luke Cage, Mister Fantastic, Spider-Man, Storm, The Thing, Thor, Venom, and Wolverine.

Better yet, this setup is a great excuse for the good guys to slug it out. The mission we saw had a team of Iron Man, Invisible Woman, Hulk, and Daredevil navigating a secret hideout to stop former buddy Cable from uploading sensitive data. En route, they battled a mini-boss — the mighty Hercules! — and lots of chaffy henchmen who fled when Hulk roared and fell nicely thanks to Havok physics. A camera that swoops close to the action gave us a good look at the impressive character detail and the gritty, more realistic-looking environments in this still-early build.

And that “Fusion” in the game title? That refers to characters’ co-op moves, which are a much bigger deal now. Each hero can launch a unique joint attack with every other ally for major damage — e.g., Hulk hurls Daredevil at foes (à la the Wolverine/Colossus “Fastball Special”), or Invisible Woman forms a bubble around Hulk and he tromps over baddies like the world’s scariest hamster wheel. It’s the very definition of Marvel Team-Up!