Speaking of Physics egnines and UE4, i loved the DMM (Digital Molecular Matter) engine used in Force Unleased, the phyics thingy that made assets get bent or destroyed according to the Material that was assigned to it.
So if you applied enough force a Steel door would bend accordingly, and you could just continue bending it if you wanted to.
I dont think i realy saw this tool used in any other games then Force Unleased and in the Tech Demo for the Indiana Jones game that never came out. But it was the most impressive thing in Force Unleashed.