RPG mod...
Please make it fun and not stupid. I've seen a few for CSS and they were absurdly stupid. However, there is one for Zombie Panic Source that was actually really awesome. You couldn't get so ubered up that the game wasn't fun, but it was enough that you paid attention to who was playing because you knew certain guys had a lot of levels and knew how to use them so you would work with your teammates (or fellow dead-heads) and make a plan to handle them. And sometimes you'd get the epic rounds where one guy (me) would be all alone with nothing but speed buffs, a magnum, and ammo-recovery to my name, leading the horde around the map twice and taking all their tickets away one at a time for the most jaw-dropping player victory ever.
On that note, I don't know really what you can do for an RPG mod in GES. In Live and Let Die, the only things I could think of giving were weapons, which only mattered because the Baron can't pick up weapons in the world, and damage buffing, which was simply based on the Goldeneye 007 handicap scale. There really aren't any other things to adjust, other than Speed, Agility, Spawn Armored, and... and I'm out of ideas.