Injustice 2 does a great job of taking an awesome fighting game and improving on it while adding enough of it's own flavour to give you something new.
It will impress you with it's graphics and a much smoother more fluid fight style making it a must own game for lovers of this genre and of super hero titles in general.
The Unlockable content Injustice 2 provides truely imense and will keep you playing it well past the point you would normally get tired of this type of game.
I'd recommend playing the first title before entering this though as the story carries on and it is so good that you don't want to miss a moment. Also it would pay to read the related comics for both titles, just because this alternate universe is one of the best DC stories in years.