I played for about 2 hours with a friend at Best Buy today. Man was it amazing, and i learned quite a few things.
-Zero has some insane combo's.
-X23 is fast as hell, and her Level 3 is nigh unavoidable (Seems like its gonna end up like Abel/El Fuerte's 2nd Ultra's in SSF4, with very few characters being able to stop it)
-Pheonix can be a wrecker of worlds, yet is as sturdy as a marshmallow
-Sentinel is still cheap
-Trish is awesome
-Viewtiful Joe plays....wierd (Something about his jump's seem floaty, and he doesnt seem to have a ground dash either)
-Galactus is cheap (The only 2 moves he used on me was a giant palm smash, and a giant laser attack)
Also, i really like the controls, though i couldnt get the hang of that aerial combo where you switch out in mid-air to keep the combo going.