Furthermore, leveling up - the heart of any RPG - is skill-based, meaning you simply practice what you like doing in order to get better at it. You'll rise quicker if you hone your character's core traits (i.e. a thief who frequently sneaks). Interestingly, Oblivion's bestiary levels up with you, further adding to the freedom as there are no "high-level" dungeons that are off-limits until you've played for 40 hours.
So like Homer, once you've begun to consume what this eternity has to offer, you'll have no desire to stop. The fourth Elder Scrolls entry is utterly brilliant and should not be missed by any adventure-spirited gamer. It serves notice to the rest of the role-playing world, unabashedly boasting, "Can you top this?"