Steve Blum is once again Wolverine and he was also Venom in the first game. David Kaye's Captain America and Nick Fury in the second game. In the first game, Cam Clarke was Thor and Daredevil. In the second, Jim Cummings takes on the role of Thor.
Luke Cage was Grim (Greg Eagles) in the first game and Cyborg (Khary Payton) in the second game. The later was also Blade in both games.
Robin Atkin Downes voices Crimson Dynamo, a non-hulked Bruce Banner, and Dark Cyclops (a sort of reprisal, as he voiced regular Cyclops for X-Men Legends) in the first game. In the second, he voices Cable for both the campaign and the DLC.
And who voices Bruce Banner in the PlayStation 3/Wii versions? Arin Hanson, also known as EGORAPTOR!
Ymir in the first game and the President of the United States in the second game were voiced by PaulEiding.
The first game's DLC was only released on the Xbox 360, thus screwing PlayStation 3 owners out of characters like Cyclops, Hawkeye, Magneto, Dr Doom, Venom and Nightcrawler. Oh, and the Hulk (The one character everyone wanted in the game but wasn't) was in the DLC too, by the way.
The second game's DLC was released, and then taken down after several weeks. For six months. It wouldn't be so bad, except a) The DLC was released over month later on the PlayStation 3, and the DLC was taken down at the same time on Xbox Live & PSN; b) the DLC was taken down before Christmas, so anyone who was getting the game as a present couldn't get the extra characters; and c) Activision had the audacity to claim the DLC was a limited offer - It wasn't, they just hadn't renewed their licence with Marvel & the DLC had to be taken down. Hell, people who worked on the game complained about this one.
The DLC was eventually made available again in June 2010. Several months after people stopped caring about the game. Unfortunatly, this doesn't apply (yet) to PlayStation 3 users outside the US, and there's no word on a release date from anyone.
And on January 1, 2011 the DLC vanished again, permanently.
What Could Have Been: The Wii version of the first game was originally intended to feature Link and Samus as playable characters.
Concept art from the first game indicates that in one level, Captain America would take his friends back in time to World War 2, and they would aid the allies on the beach of Normandy. Talk about Best Level Ever that never was.
Electro is present in one of the villain concept art pieces in MUA 1, but was not in the game. Guess who shows up early in MUA 2?