i posted an idea for a halo rpg in a thread spectral jester made a long time ago, so i guess I'll re post it here
my game would be a cross between halo:odst and Fallout 3. it would be a fps rpg set in the halo universe and you would play as a marine. you could buy different weapons and different armors like maybe the army body armor or the marine body armor or odst armor, and of course there will be vehicles you'd be able to drive, it could take place on harvest early in the human-covenant war, and you would get quests where you would have to defend cities from attacks, attack covenant bases, reclaim areas taken over by the covenant and maybe there could be a battle on board a covenant cruiser or a unsc frigate or something like that. you will get exp. for kills and completing quests and you could get abilities to make your guy better like increased accuracy or the ability to dual wield pistols, increased movement speed, carrying capacity and other things like that.