Really though, why does nobody think this game has the potential to suck?
The developers have been incredibly open about showing off the game at various events and answering user questions and thus far the game simply hasn't come away with much in terms of negative feedback from the people who've played it. You've got a lot in terms of open endorsements from people who play these sorts of games competitively and I think that's another reason why people are just getting really excited about the game's prospects.
I've been personally following the games development since MikeZ was first showing it off at Family Fun Arcade (back when Filia was the only playable char) and I just come away from each quick look impressed with the level of thought that's seemingly went into every facet of the game. It's especially exciting for those who, lately at least, have been sort of dissatisfied with the fighting game offerings from companies like Capcom as well.
I guess what I'm trying to say is, if the game does suck, why haven't we heard that fact from the literally hundreds of people who've been able to get their hands on the game up until this point?
What did he fix? Serious question.
The infinite prevention system and doing their best to make sure that characters aren't just categorized as assist characters are probably some of the biggest fixes to the system overall. Though it wasn't necessarily a problem in MVC2 you could also say the addition of custom assists has enhanced the team based system overall. I love Marvel 2 as much as the next guy but it's pretty hard to argue that the game isn't basically held together with bubble gum and bandaids.