Concerning additional weapons:
IMO Xaser's list seems a little overboard for a single map and I'm not really sold on the idea of replacing the entire arsenal either... we don't want to turn this into a TC, do we?
I think the hand grenades, the unmaker-kind of weapon and the flamethrower could work well, as they have their own purpose/niche when compared to the original weapons. I like Gez's suggestion for the Dark Claw better than having a flamethrower though, because using the latter feels unstatisfying when the monsters don't have a proper fire-death-sequence!
Just my 2cent