One of them has a mouth that splits open, the other doesn't. Right?
Have you ever wondered the difference between the zombies in Dead Rising to those in Resident Evil 5? Wonder no longer because Dead Rising 2 producer Shin Ohara has broken it down.
As far as Dead Rising goes, zombies are dumb, basically. In Resident Evil, zombies are an enemy that you fear because they’re strong and you have limited ammo. For Dead Rising, a single zombie doesn’t scare you, but when there are a whole bunch they could do a lot of damage.
The whole idea with zombies in Dead Rising is they are not something you have to fear, but something you play with. More of a play thing where you pick up a weapon, go to them, and you want to test out that new weapon. In Resident Evil if you pick up a weapon you want to save it, you don’t want to use it unless you really have to. Dead Rising is about having fun with zombies, trying out different weapons.
If you expected something you hadn't already thought of, we apologize.
Source: Capcom Unity