The Aliens rush you quickly (think Left 4 Dead) and are devastating up close. I tried this mod myself, using it to play a mission right after I had played through it using vanilla settings, and it definitely seems like some steps have been taken in the right direction. Some of the shading and lighting has been reworked for the new mod.
A new Aliens: Colonial Marines Overhaul Mod has been released! A “Boiler” Alien hides in the shadows.