It seems to me that it takes more bullets and thus more time now to get cars, big red tanks, and petrol stations to blow up. Its harder now to time those explosions in order to damage the machines who walk passed those cars and such.
I noticed that too. It takes some of the fun out of blowing up cars and fuel tanks. If you do manage to kill a Hunter with an explosion, you can be sure he had time to write his Will first. The worst part is how hard it is to destroy the field generators on a Reaper. You have such a short time to shoot and nothing happens.