One of my favourite features of Final Fantasy XIII-2, time travel allows the player and their party to jump back and forth between different eras in the game's history, small self-contained 'What If?' scenarios filled with stories to experience and items to collect.
For fans of the Final Fantasy XIII setting, XIII-2's different time periods are a veritable smorgasbord of new background information, further fleshing out the fiction of the game. Each new area grants a fresh perspective on the world and its people, neatly tied into the main storyline in creative ways.
And for me? Well I am OCD about collectibles, so giving me separate locations with a set number of treasures to find appeals to me on a primal level.
I just wish there was a way to make the game play the Doctor Who theme every time that portal opens up. OOOOOOeeeeeoooooo.