I don't really remember any physics in Dead Rising. Maybe I'm wrong, but weren't all the death animations scripted? I can't remember any bodies flying around or anything. Could be wrong about the graphics, in terms of textures, models etc. It's been a while since I played Dead Rising, but I wasn't blown away by anything other than the sheer number of zombies on screen. I have sort of the same impression of Crackdown 2.
There are spots in Crackdown 2 where there are easily several cars and thirty or so AI (pedestrians, cops, enemies) on screen, all getting blasted through the air by rolling vehicles, charging players, explosions, UV gun etc. When you get the charge ability, you can run down a street smashing everything out of your way. The cars, light posts, parking meters, bus stops, dumpsters will slam into people and send them flying. I'd say there is a lot more going on in terms of physics than Dead Rising, by a long shot. Yesterday we started playing baseball. One guy would pick up a light post and another guy would throw a car door, a corpse, or whatever he could find as the ball. It was hard to do, but if the player connected with the hit, they'd absolutely launch the object down the street. You can also do fun things like grab the car your friend is driving, while he's in it, and chuck it on top of a building.
It was pretty fun. I'm still not sure I'm 100% sold on the game. I'd like to see more variety of objects, with different purposes, in the game to expand the sandbox mentality. I think there are some guns or weapons I didn't have access to, and I don't think all the vehicles and weapons are in the demo. I could be wrong.
Just Cause 2 would have been great with co-op to absolutely do weird things. That's one thing Crackdown 2 has right.