UMvC3 has great visuals (art style and graphics) and a control scheme with mechanics that are easy to learn. This makes it very welcoming to new comers. The ability to mix and match your favorite heroes and villains has also returned. When you have a couple of friends to play with, it's almost impossible to not have fun and end up screaming when playing this game.
However in comparison to MvC3, this is a really lackluster effort at an "improvement" and did not live up to the hype as MvC2's successor. The single-player mode is very weak, practically limited to training mode and arcade mode so it isn't hard for people to lose interest when there is no one to play with.
As a stand alone game, it's worth a buy if you're into over-the-top animations and want a fighter that's easy to learn. Just keep in mind you might end up getting bored after a while if you don't play online.