When I bought it, I played about 30 minutes of Marvel Ultimate Alliance 2, hated it, and threw it in a drawer.  I found it the other day and put in about six hours or so:

• The storyline is boring, then good, then reaaaaaalllly bad.
• X-Men Legends 2 really blew out the customization aspect of the game.  Since then, they've been dumbing it back down, which I don't like.
• Thank God you don't have to go to a checkpoint to change up the team.
• It's really annoying that you can't use everyone, and certain upgrades are locked out depending on which team you choose.
• They really dropped a lot of characters from the roster, while only adding a few new ones.
• Who the fuck is Penance and why is he in this game? (I actually know the answers to both questions, but he's still lame).
• I'm totally going to go back through this to get more achievements.