Good question. I never got to play it because the servers were down for me then I went out with a friend.
But from what I did, there is some emblem customization. Thers a border layer, then a background layer, then 2 symbol layers. You might be able to get more symbols, idk. From what I saw, you couldn't move the images around at all, so that was pretty weird.
You can change the appearance of your regular character and your villain character for online. Theres some unlockable costume bits as you level up and i think do some challenges as well.
Theres quite a few modes, including an new hardcore one, which has no perks(called boosters in the game) and none of some other stuff, and probably less health.
Oh yeah, boosters. You get money to buy these things called boosters, which are perks. You have 2 slots. Then theres some other slot thing. You can get an RPG(I think thats what it was) right off the bat to put in there, but as you level up theres more things.
Thats really all I know. I don't know the max level, how much of that was in UC 2, and how the game actually plays.
With all these new features, I'd assume maybe the multiplayer is more of a frontrunner in this game over the campaign. Maybe not though...