The pros and cons that I see in the MvC3 trailers:
Pros:
-The controls look MUCH tighter and more responsive than TvC's, which was a big problem in that game. Already this game looks like a lot more fun.
-The graphics are pretty nice.
-It's nice to see how a lot of the battle mechanics from MvC2 were brought over
-Damage scaling is almost what it was in MvC2
Cons:
-The voice acting is ATROCIOUS. Seriously, I pray to god that there's a Japanese voice option of some kind. Chris Redfield and Deadpool are particularly annoying.
-People who complained about MvC2 being broken aren't going to like this game much better. =P The game's ridiculous ground bouncing juggles allow for easy near 100% damage combos that look like they don't require very much effort at all.
-What did they do to combat the above problem? Why, reintroducing combo breakers, of course! But not just content to combo break, they also made them work like parries, allowing you to do a combo on someone in the middle of their combo. The stupidity of these gameplay ideas boggles my mind.
I don't know what Capcom is thinking with some of their game design choices here.