These little features don't really add all that much to the overall gameplay, but they are nice little touches, like garnish on meat and potatoes. The meal is still quite substantial, but the presentation doesn't make us go 'wow'. If the previous MUA didn't have them, I wouldn't have been looking for them in this one. But to remove them from the follow up is short-changing us players on quality while substituting it with, um... nothing. Well, the control system is easier to use, I'll give them that.
Ok, anyway, I think the best characters to have on the team are either Iceman or the Invisible Woman for powerful ranged attacks, a psionic like Jean Grey or Psylocke who can fusion with a bruiser like the Thing or the Hulk for a player-guided "Billiard Ball" attack (creates a hamsterball around said bruiser who then charges masses of enemies for huge damage -- even bosses don't stand up to this kind of assault for long). The fourth member can be just about anyone else, 'cos they're just coming along for the ride.
Don't get me wrong. I am having loads of fun with MUA2 as it is. There are still lots of team combinations and fusions I have yet to try out, and side-quests yet to conquer. They haven't taken the best bits out of the game, but it could have been so much tastier.