Ah, Elder Scrolls: Oblivion. A game that can easily eat away hours of your life without you noticing or caring all that much. It may make you cold to family, ignore friends, and even forget to feed your pets but you can never stop loving it. Why is this? Is it because it's not only full of fantasy elements but also adventure, mystery, romance, horror, heroism, fear, and vengeance? Is it because you can customize your character, choose how good, evil or neutral they'll be and dress them in a vast array of outfits, armour or none at all?
Whatever the reasons are, they are all good, for this is Oblivion, and Oblivion is good.
But seriously, this game is really addicting. And unless you have a strong enough will to pull yourself away you may end up engrossed in all the sub-plots, side-missions, and random Daedric god statues that talk to you. Oblivion's massive open-world leaves the story entirely up to you, you can choose to complete the main story arc first or do pieces of it here and there while going off to discover ruins, caves, and settlements.
This kind of game design is a smart one because it doesn't force the player to do one thing at a time. You could have at least ten different active missions and none of them have to be done in the order you engaged them at. Even when NPCs tell you to hurry, there really isn't a need to hurry because everything is pretty much dependent on you being there. Oblivion allows you to make your own Elder Scrolls story any way you like, with any available race you like.
