I always thought the main quest was to sort of a way introduce people into a open world in a game like the Elder Scrolls. It helps lead people to new locations and features they might not have discovered on their own. A good main quest in a sandbox game should encourage players to explore other aspects on the game.
That being said I believe Oblivion's main quest serves this purpose well enough. My first play through (after a quick bit of exploration to familiarize myself with the controls) I followed the main quest in a fairly linear manner in till I managed to get Martin to safety, at which point I get completely sidetracks by all the other wonderful content I had glance over on my way there. And after having my fill of exploring I decided to finish the main quest out of a sense duty. I imagine I'll do something similar with Skyrim, perhaps completing the main quest in till dragons are released before fully exploring the rest of the game.
That being said I believe Oblivion's main quest serves this purpose well enough. My first play through (after a quick bit of exploration to familiarize myself with the controls) I followed the main quest in a fairly linear manner in till I managed to get Martin to safety, at which point I get completely sidetracks by all the other wonderful content I had glance over on my way there. And after having my fill of exploring I decided to finish the main quest out of a sense duty. I imagine I'll do something similar with Skyrim, perhaps completing the main quest in till dragons are released before fully exploring the rest of the game.