Oh god. Just finished playing that game on easy. That's a lot of monsters and I was only playing on easy!
Ended up using machine guns for almost the entire game. My machine gun skill was 115 by the time I finished after you took into account the implants I was using as well. The top machine gun dealth 180-210 damage with a massive rate of fire. Once you pick up the Volcano you can pretty much run straight at a mob of any size of anything smaller than the rocket launchers and not have anyone come near you.
Wow, 115 is pretty high. My weapon of choice was shotgun and my shotgun skill was 65 without using any implant whatsoever.