So the demo came out for this, at least for 360. I'd assume it's on PS3 as well but I don't have one to check. (Edit: Apparently not on PSN yet)
The demo consists of a local multiplayer option and a single player mode. The single player is a short version of what I assume the arcade mode will be. You fight a very short series of opponents that are available in the demo and it ends in a fight with Doomsday. I don't know if they already announced this but the available characters for the demo are Batman, Wonder Woman, and Lex Luthor. Unless I missed it I don't think it lets you remap the buttons on your controller in the demo. I can see where you remap your controller in the options menu but can't select it. So that might be annoying for people who use 3rd party controllers for fighting games.
The gameplay feels very much like MK9 with stiff animations and a built in combo list. If you didn't like MK9, I don't think this game is going to change your opinion on NetherRealm's style of fighting games. However, it will probably still be the best fighting game to feature DC characters because well their track record for this is crap. It would be hard not for this to be the best fighting game featuring those characters.
My one major complaint so far is the way the life bars work. When you finish a round they don't reset to put you on even footing. The winner retains however much life he has remaining from the first round going into the second. In this way the loser of the original round will be at a disadvantage in health and be fighting an uphill battle in the second round. I know this isn't the first fighting game to do this, but being a DC Superhero fighter it's going to appeal to a very large casual audience. That type of life bar is very anti-casual player in the way it works. It's going to make getting into online play extra difficult for those people, and this is a game that should be trying to appeal the most to the casual fighting game player market. My only other minor complaint is that I hope the full game has more options for what the winning character says after the match. If not we'll be hearing "stay down" a lot.
So I have some complaints, but overall I think it will be a game I enjoy. What do you guys think?