When they get shot/blown up/burned they should just light on fire or simply be disabled, not blow-up like they are made of C4.
This isn't Fallout. This isn't Hollywood.
Don't make cars explode. Mythbusters have set this in stone for us. It makes me icky when it happens.
Just make sure that when blown-up with explosives they still jump in the air and roll. It's happened a couple of time to me that they rolled in my direction or on top of me, but didn't squash me because there was a box or something. My friends spectating loved it. It was like a scene from a movie. Such sights (with dismemberment and corpses flying through windows and doors) is one of the reasons this game is so awesome.