A sleeker, refined version of the original.
MUA2 feels like MUA with many of the little annoyances removed such as the accessive load time to access the character screen during combat, the reliance on God of War style button press sequences on virtually every boss battle, and the constant management of team equipment to combat enemies with various immunities.
This time around we have a simpler interface. Less item management means more time spent mashing those buttons and clobbering wave upon wave of bad robots, bad soldiers, and bad robot soldiers. Soon you battle a cool boss and end up back at your HQ to mix things up with a challenge mode or a trivia game. This is all very fun due to the great selection and variety of marvel characters.
MUA2 is the same or better in all respects to MUA.
I noticed two carried over flaws-
1) enemy characters/bosses will occasionally get stuck out of the combat area forcing you to reload (happened to me once so far)
2) Some characters voice acting is weak and sounds mismatched. Notable are Thor and Venom.
Overall MUA2 is great fun and I recommend it to any fan of Marvel heroes!