I'm not a huge pro of the fighting genre games, mainly because they're usually overly complex and difficult to master. But Injustice combines the awesome fighting genre style of a Mortal Kombat and MvC but made it simpler and more fun to play for the average gamer.
Injustice has all kinds of different modes where you can play as a ton of characters from the typical Batmans and Supermans to some of the rarer comic heroes and villains I've seen. The fighting gameplay is very fluid and doesn't take months to master a difficult control scheme like other games such as Tekken and Super Street Fighter.
Some unique aspects to the game are actually the level designs themselves. Each level has a certain number of interactions you can manipulate. If the level has hanging objects from the ceiling, you can often times use those to throw at your opponent for serious damage. Also, you can use a special power kick to send them flying through the level's own barriers, leading to a small cut scene that has the enemy flying into another map. You can then continue fighting from that location.
Because you can interact with the levels and certain objects, it makes it easier for any player to use. You can remember locations of objects on maps and use that to your advantage instead of memorizing a boatload of button combos. Of course each player has sick combos and special abilities though too.
Like MvC, each player can unload a super special ability once his power meters are all filled. You can fill them by doing certain special moves and taking damage, etc. There are also unique "clash" sequences where the players clash in the middle and battle over power meters; you can bet a set number of filled meters and either gain health or steal their health. It's somewhat interesting.
But overall it's a solid and well polished fighting game, for those who enjoy this genre. I liked the variety of characters and ease of play the most.