The block stun is absolutely ridiculous. I don't remember it being an issue in MK9, but it definitely reared its ugly head in Injustice. If you blocked Hawkgirl's mace charge it literally felt like time stopped all around you and there was nothing you could do until she ever so lightly landed back on the ground.
It also doesn't help that the block stun is all over the place. Some moves have it, others don't, and some are basically a just frame punish with none. With the amount of specials/attacks in this game some consistency in how to punish would be appreciated.