Taken from hadoken:
Remember the full rpster leak of Super Street Fighter IV? what about the leak of the roster of Tatsunoko vs Capcom? well, it appears no capcom fighting games is safe from those leaks, as apparently, the full roster of Marvel vs Capcom 3 has been leaked via a website glitch.
The list of the characters was spotted via the flash source code of the official game website, and has since been deleted, which adds more fuel to the burning fire. According to that list, this is the final roster of MVC3:
Marvel: Spider-Man, Hulk, Wolverine, Mr Fantastic, Captain America, Iron Man, War Machine (alternate Iron Man outfit) Elektra, Thor, X-23, Magneto, Dr Doom, Shuma-Gorath, Emma Frost, Deadpool, Super Skrull, Taskmaster, Juggernaut, She-Hulk
Capcom: Ryu, Mike Haggar, Frank West, Chuck (alternate Frank West outfit), Spencer (Bionic Commando), Dante, Chris, Morrigan, Arthur, Amaterasu , Albert Wesker, Zero, Chun-li, Viewtiful Joe, Trish, Tron Bonne, Hsien-Ko, Akuma, Felicia
Looks like Venom will be DLC.
Holy ---steaming pile of meadow muffin--- thanks Hyper. Oh man oh man. I cant wait, even though there are some stupid choices for new characters. X-23? Emma Frost? She Hulk? Lame. Dont even get me started on the Capcom guys. I dont even know who half of them are.
Oh bootay! How is Sentinel looking? Is hiyato in there too? I got a chub when you mentioned Galactus. Is he rad looking, or do you just fight his hands or something? Or does he do kind of an Onslaught thing from Marvel vs Capcom?
How the hell do you have it already anyway? 
Yea, some of the character choices were kind of lame...I don't mind She-Hulk so much but X-23? yea that's pretty lame. On the Marvel side I think the characters are fine for the most part but I would have liked to see The Thing or Human Torch or anyone from Fantastic Four who have yet to make an appearance in any of these games. Thor was a good addition although I do not like his controls and his moves seem a little underpowered.
As for the Capcom guys...yea there is some suckage...why do we need 2 guys from Resident Evil? And why the guy from the ---smurfy--- Bionic Commando remake? Tron Bonne is fine but why no Megaman?!
Sentinel looks pretty much like the 3D version of the 2D version..and the controls are pretty similar too.
Did not see Hyato yet.
Galactus is not playable...and when you fight him you are standing on a ledge and he is only shown from the chest up....so you fight his chest, head and arms.
I have it already because i have a modded 360 and games always get released ahead of time on the pirate scene. It just got released somewhere else before USA is all and someone ripped and released it Region Free so I can play it on my 360. Happens quite often. Like I said before, I use the modded 360 to test games out and see if they are worthy of a buy for my unmodded one. If a game is just ok....I will keep it around until I am bored with it, if a game sucks I won't and if a game is epic or worthy of Xbox Live play I will buy it.
I would definitely say MvC3 is worthy of a buy.