Feels really nice, although I'd like to see the barrels move more when shot. Perhaps they don't move so much at first, but leak their contents when shot and then move more the emptier they get...?
The cool thing is that it's so easy to do with a good physicssystem. It's just a matter of fiddling with the mass of the barrels.
I know it's just a test but try making the barrels and boxes fly away from the grenadeexplosion, that would make it look even better.