I've played through the main quest twice now. Once with "minimum leveling," finishing out at level 5 and once with a leveling mod, finishing out at level 17.
I've reached level 20 and gotten my first piece of glass... but with the main quest gone by I'm a Champion who can get away with about anything. The secondary quests, which I was looking forward to, all seem sort of hollow. As opposed to Morrowind, where I spent all too many happy hours pre-and-post Neverine wandering from island to island and poking my nose in. (I even played a mod that made Juib the Neverine and left me free to be a tomb-raiding tourist.)
In Morrowind, ashstorm and daedra damage was semi-contained by the ghostwall and Caius would slow down the Neverine, telling him to make himself known and get some experience under his belt before handing out the next step in the main quest. The plotline wasn't in your face, you weren't sure you WERE the Neverine until most of the way through (if ever, actually) and knew that it you pushed ahead too fast you were NOT advancing the cause.
In Oblivion, the main quest is more driven by the Gates opening in populated areas. I tend to play a conscientious sort who can't forget the damage the oblivion gates and wandering daedra are doing long enough to take a working vacation to furnish a house or reunite lost twins. So I did my duty and closed the Gates... and now the thrill is gone, I *miss* Martin, and it's time to pick out drapes. Um. Can you say anticlimax?
With Oblivion's default levelling system, pacing obviously wasn't a option -- whenever you hit a gate you hit monsters at your own level. With leveling mods and the various experience rewrites, however, it should be.
Are there any mods already written that stagger the Gates appearing? Maybe only popping up around one city per week, or per 3 player levels, giving time for role-players to round out their characters and build up their resumes as something other than the Hero of Kvatch? (This approach means rewriting the various Counts' motivations if you went to look for troops for Bruma in a city that hasn't been targeted yet. The Counts would have to put you off with not sending men to Bruma when their own cities *might be* targeted at any moment...)
An easier to implement alternative would be to slow down the pace by making the various translations of bits from books take a week or longer instead of a day. In the meantime you are told to go away and make yourself useful to someone. Giving you valid, plot driven 'down time' to explore, build up your skills and your rep... or pick out drapes.