How do you counter in assassins creed 3?

Whenever I push B to counter it goes into that slow motion phase but it won't let me actually counter kill. Yet it let's me counter kill with the hidden blade when I try to disarm them! Why would it kill if I'm trying to disarm someone? I'm getting furious because I have to constantly push X in order to kill someone in the game. Like I said I try to counter an enemy and it just won't let me counter. I actually found this game to suck so far, it takes forever to get to the Indian guy as well as it takes forever to get the assassins clothing on. But it also only allowed me to counter with fists in the very beginning.