Come on people, embrace this new style of gameplay! They could have done the same 'ol, same 'ol tried & true, but decided to mess with the formula a little bit.
I give it thumbs up, I'm all for innovation.
I don't think this really qualifies as a "new style of gameplay. It's more like taking established gameplay and adding lots of context sensitive weapons.
And that "72 hours" is obviously not real-time. According to IGN's preview:
Roughly, an in-game hour takes about five minutes to expire while not in a cut-scene, of which there are many. After spending a number of real-time hours with the game, it's clear there'll be less free time available to kill at random than we originally thought.