Man, "Injustice" is just too much fun. There is so much content here it's insane - that they're going to keep releasing characters and maps is awesome. Very cool that Lobo will be coming soon - honestly I'm surprised he wasn't in the core game, he seemed totally up the MK team's alley.
I beat the story pretty quickly (it's like a long, middle-of-the-road "Justice League" episode), and am now playing through the "Battles" section.
"Battles" contains a few dozen (!) variations on the standard MK-totem, where you choose a character and fight through 10 others. In the Classic Battle mode, it always ends with Superman. I'm currently playing through Classic Battle with 20 characters. So far I have done (in order):
Nightwing
Hawkgirl
Bane
Raven
Solomon Grundy
And in MK style, each character gets their own little ending. Some of them are pretty neat (fan service-y, but cool if you're into that kind of thing), and some a pretty dumb.
The same can be said for the characters' signature Super Moves. Some of them are mind-blowingly awesome (I loved The Flash), but others are strangely uninspired and boring (Wonder Woman...what the hell?)
The number of costumes available to unlock is daunting.
I do find it a little irksome that so many of the costume unlocks rely on owning other devices (many of the costumes require playing the iOS game...I don't have an iPhone), but I'm sure they'll be available for download in the future. The one I am most bummed about not being able to get at this time is the Batman Beyond costume.
The character I find to be almost universally the hardest to fight against is Aquaman. He has a few attacks that are just so fast I am never able to block them, and he also has this throw that he is able to follow up with a juggle combo and it just destroys.

