They said many time during and after E3 and leading up to release that this "epic story" is supposed to be YOUR story and MY story unique to each individual. To do that you need a fairly loose narrative. How about Elder Scrolls? Or Fallout? Both critically acclaimed games and loved for the lore of the universes but most of the lore is found by exploring the game world and doing side quests some of which can be incredibly difficult to find. Meanwhile the main story is rather simple with no real depth and pretty short if you burn straight through it.