• Hulk
• Hawkeye
• Cyclops
• Nightcrawler
• Dr. Doom
• Magneto
• Sabretooth
• Venom

All characters will have their own costumes, movesets, and powers, and there will be new teams and combo points that take the additional characters into consideration.

Given how the shipping version of the game didn't really acknowledge your characters (like Hank Pym talking to Captain America about Captain America, in the third person), I'm sure the inclusion of Dr. Doom (the main baddy and "Big Boss" of the game) is going to play a bit wonky. But we fanboys can pretend one or the other is an advanced Doombot. Or something.

The packs'll cost you 500 Microsoft points ($6.25) each for the Hero pack and Villain pack, or you can get them together for 800 Microsoft points ($10). But they also added 12 new Achievements and 250 additional Gamerscore points

Check out Marvel.com for screenshots, and they're promising new info on costumes and powers between now and April 10.

UPDATED: Delayed and MIA, with no ETA, but I want the content ASAP. (More useful info at Gamespot.com)