Embargo's up, so here's what we know:
Final roster will be approximately 30 characters.
Confirmed 3D models on 2D plane, like Street Fighter 4.
Teams are 3 on 3 like MvC2 instead of the 2 on 2 from TvC.
The leaked list of characters was apparently fake (or at least only inferred from the silhouettes behind the logos in the trailer, because Capcom is only confirming the 6 characters in the trailer right now (Wolverine, Iron Man, Hulk, Ryu, Morrigan, and Chris). However, they've also released a bunch of art with more silhouettes, which has led to a bunch of crazy speculation, including some comic characters I've never fucking heard of.
So rumored characters include:
Marvel: Deadpool, Captain America, Black Widow, Super Skrull (?), Mephisto
Capcom: Felicia, Frank West, Dante (or possibly Nero, they look almost identical after all), Seth
Also the bad news: release date is 'Spring 2011', for 360 and PS3. So it's at best a year off.