A terrific game not for it's main quest, but for the details.
The customization in terms of physical characteristics is pretty much where the game starts. One gets to select a race from the many Races of the Elder Scrolls World. After this you are thrown into the game, following an NPC into combat, protecting him with your life. Near the end of this little game-starting adventure, a class is selected based on your style of fighting up to that point. After which you have the opportunity to assume the estimated class, select another from a list, or create a class of your own.
After this is done you are asked to leave the sewers (the location at which your adventure has been taking place) and thrown into the great wide open.
Your compass is leading you towards completing the main quest. But you've got a whole world to explore!
So you can go about the game in any way you wish from that point on. Go join a guild and move up the ranks, fight your way to become champion of the arena, or begin exploring to complete the sacred Daedric quests.
Whatever you choose, you'll be living life in the world of Cyrodill, and so immersed in the deep lore and complex factions that you wont realize you have to be up for work in three hours.
All in all, there is no way one can put the terrific aspects of the game into one review. But the only word that comes to mind is: 'unforgettable.'