I'm kind of running out of steam on this one, too. Don't get me wrong, its fantastic, but to be perfectly honest, I think the quests/storylines in Oblivion are far superior to Skyrim's. For a game with such an expansive, beautiful landscape, why do you have to spend so much quest time playing in caves?
Don't try complaining about adventuring in Dwemer ruins or ancient Nordic crypts

They're pretty badass, and for the most part, completely optional. A lot of the game is tied into the history of Skyrim, which is buried in these ruins (obviously)
IMO, this is how it plays out
Warrior-esque guild: Skyrim
Thieves Guild: Oblivion, but Skyrim's has a pretty sweet twist
Mages Guild: Skyrim
Dark Brotherhood: Tie
And Skyrim has the sweet civil war questline which is far superior to Oblivion's arena IMO.
The main quest, I'd give to Skyrim. It was much more interesting and fun, and less "busy work". An evil badass dragon won't wait forever in destroying the world, ya know. No need to make it longer than 20 hours worth of gameplay in that aspect.
Skyrim is far superior to Oblivion, IMO.
IMO, JMO, HIJKLMNOP, ETC ETC