Taken as Elder Scrolls games, Skyrim is leaps and bounds better than Oblivion. Taken as just games, both are still fun, but Skyrim is superior.
Heck, Oblivion is just a sterile game with ugly environments [i.e. nice for its time], rotten potatoe people, a counter-intuitive [i.e. turrible] level up system, bad writing, 'blah' quest design, overall awful dungeons/caves, and o.k gameplay. Didn't stop me from putting 500hrs into it though.
Modded Skyrim may even dethrone modded Morrowind once Skyrim hits its prime. Oblivion... never gunna happen...