Dorian Cornelius Jasper said:
Beat the game.
With vanilla Oblivion's broken difficulty scaling, it's completely plausible to finish the main storyline at level 1 even.
Sorry for the double-post, but I had to address this:
Note that finishing the main storyline is easier at Lv2 than it is at Lv1, not because the character is stronger, but because getting the Daedric artifact for Martin as part of a quest is easier if you can do a simple quest like Sheogorath's Wabbajack quest rather than having to pull off the aforementioned killing of Umbra (allowing you to circumvent the Lv20 restriction on Clavicus Vile's quest---see UESP.net for details.)
Beating Oblivion at Lv2 is ho-hum. Doing it at level 1 is a feather in a gamer's cap.