One of the most notable things about the Dead Rising series has been the fact that you're forced to play the game strictly against the clock. It's divisive, but it makes Dead Rising what it is, or to be more accurate, what it was.
In an interview with the LA Times, Dead Rising 3's executive producer stated that the whole missions-against-the-clock thing is a thing of the past, stating that "The past installments were relatively regimented and you were kind of forced along at a particular rate of time. Now we’ve unlocked that to really let you explore this world. We went deeper with more stuff to interact with, more areas to explore, it just feels like a much richer world as a result."
I'm a little torn by this. On the one hand, it's unfair to judge a game before it's out, and the prospect of a totally open-world zombie-fest still has some appeal. On the other hand, the clock-based mechanism in the previous games was such a core part of their appeal to me.