Good news, the Shooter and Role Playing Game (RPG) genres are not cousins.
Thankfully this fact means that their recent child - Borderlands - is not an inbred freak. The game might remind you of Fallout 3, however, there is less narrative and character choices and far better and more traditional shooting mechanics. So, basically, it takes the shooting mechanics from Halo/Call of Duty and combines them with the open world quests and loot of something like World of Warcraft. Of course the downside of this is each genre seems to carry with them certain faults.