First of all I want to say that I'm a big time fan of Insurgency and have played it alot, it's got loads of features which were always on my wishlist in an FPS shooter.

ONE thing I have never seen done by any video game and I was hoping to see in Sandstorm was to have any kind of smoke not being able to go through the walls and stay in the room only able to escape through windows.
It would give a feeling that there is an atmosphere in the game and just like the effect on grass and trees from the air and wind. Smoke should be effected by it to.

Just wanted to share my thoughts.
All the best.