MUA2 isn't as exciting or epic as MUA1, but surely worth playing.
About the only similarities to the two games are the hack and slash button mashing - similar to the genre. The rest is pretty unique - I'll leave it up to you to decide if it is better or worse.
In MUA2, the story is kind of week. I never read the comic series it is based on, but I didn't feel the differences were really believable, or strong enough to drive a wedge between the meta-human population. I didn't buy it - it seemed out of character for some of them.
In MUA1, I was able to unlock three costumes for each character. In MUA2, there is only one costume for each character. Most of the replayability in MUA1 was so I could see all the costumes - and they were cool. I think the alternate costumes in MUA2 are weak.
Even the fusions get boring relatively quickly. I may be selfish, but I don't need Deadpool stealing the thunder from Thor - my character of choice in both games.
One thing I did like, is that reference was made to MUA1s story line. I wish it would have went somewhere though. The things they mentioned I was very excited about seeing how they played out now. It never happened.
All and all, a good game for the genre, but a miss compared to the original game.
UPDATE: I just finished the game on Legendary difficulty, and it was pretty much pointless. It was nice seeing the couple of boards that are from a different perspective (and a different ending), but not worth another 10 hours. I would have stopped half way through if it wasn't for the achievement points. Stick with MUA1! There is way more replayability with the first game.