Injustice is basically netherrealm's thin excuse to re-skin and re-release the same engine it used in Mortal Kombat 9. In essence it was a way for them to do as little work on the engine as possible while using characters that would get a broader audience than their flagship series. This is both a good, and a bad thing.
The good: It's pretty. The graphics shine in all the right places, the interface is pretty much flawless, and there are more than enough options to tweak pretty much every aspect of it. The story mode is worth playing, and there's more than enough single player content to justify an 'offline' user's purchase.
The bad: The same awkward, almost clay-mation-like animations from MK9 are still here. In fact if you stood fifty feet away and squinted you'd be hard pressed to identify whether what you were seeing was Injustice or MK. It really is THAT similar in gameplay and animation.
Now, I'm a hardcore fighting game fanatic. I've been playing fighting games since their inception, and hope to continue to do so until they, or I, cease to exist. As a hardcore fighting gamer I have a problem with Injustice being so brutally unbalanced and biased toward momentum. Like all netherrealm games there are only a handful of viable characters, and it's all completely juggle based combat. That and the fact that lifebars don't reset between rounds is a rough sell to a casual crowd.
Now ALL that said: I see this game a lot like I saw Street Fighter X Tekken back when it first came out. There's a good game in there, and it'll take a few updates for it to show up. If the characters get balanced a little better than they are now all faults can be forgiven.
Anyone who is thinking about buying will also want to keep in mind that Netherrealm has made no secret at all about extensive character DLC.
So is it worth buying? Yeah, but only if you are a fan of both DC AND the MK9 engine, and slighly gimmicky fighting mechanics. Otherwise, skip it.