It's nice when in a fight that being on fire doesn't make you roll around in pain as it does in singleplayer, as otherwise players could kill you easily by just letting you get burnt a little bit from an explosion, or molotov, or petrol and you wouldn't be able to move to defend yourself.
But it's also weirdly unrealistic that your character stands in a blazing inferno, obviously dying, but making no noise and still standing there firing his carbine.
It would be nice to have more ragdolling. At the very least I would like the ability to jump and ragdoll yourself as you can in Singleplayer. I miss just dive-bombing pedestrians on the street.