I think it would be awesome if we can have more particles for explosions. It would be cool to have like more rocks/pebbles that fly around and bouncing everywhere. When the pebbles hit the ground, it makes a mini explosion as well, like kick up dirt or bits of concrete or grass. It would be even awesome if we can have sound effects for the rocks/pebbles that fly around, like "PEW" when a rock bounces off concrete at high speed. This is not a particles department, but it would be a nice touch ^_^
Particles + anything collision related: FPS rape. So better not :D Valve can only do that impressive physics stuff, because its precomputed and it can only be interacted in certain ways with. So there is not really a chance to get anything bouncing around like that for us.
I can do this and it's not really that nasty on FPS since not much else uses that stuff, but it's pretty negligible and rarely noticed, as well as the fact it's really really fucking hard to tweak the bounce + slide options to bounce realistically.
Fixed. Empires needs more smoke, and it needs to be as opaque as the US government so that no one can see anything.