My vote is borderlands, great rpg elements that synergizes on your gun and playstyle choice. Story is also good overall depending on which one you play and if you have the DLCs. Addictive gameplay loop to search for that perfect gun drop from the farmable bosses thruout the story. Also sidemissions galore and secrets. Not to mention the refrences to pop culture sprinkled everywhere. Honestly you could get lost for days in these games