Graphically it is a lot better than the first Marvel Ultimate Alliance. It is not the cell-shaded comic drawings that they had in the first title. Instead it is more detailed, utilizing dynamic lighting for not only the stage, but the characters as well. Another big difference in the game is the power fusion attack. Something that you will be able to use in combination with any of the 24 playable characters. Think of them as combination powers used between two heroes/villains to make a more powerful attack. Also a step up is the power boost will boost your entire team, which is a really nice addition.
One of the things I was impressed by, is that there will be dozens and dozens of enemies at the same time on screen. The online co-op will be nice to use when you are going through the game with your buddies via PSN or XBL. Especially now that when you save your progress, not only the host will be able to save but all players will. That goes for trophies/achievements as well. Also having Deadpool in it will help also and is possibly the best addition to the game. Deadpool even mocks you as the player as you go through the game, keeping true to his persona from the comics.
My overall impression of the game is that it will be worth a pick up just to see how the storyline will play out and how each character will interact with each other as you get to choose which side you want to assist. I will be able to talk more about it as it gets closer to being released.