Oblivion definitely had its moments. If modded properly, I'd say it comes very close to Skyrim. There's even a mod that makes the leveling system much better. Though Skyrim looks prettier, has a better leveling system, better combat and arguably more content, Oblivion shines in many areas: for instance the soundtrack, overall mood and ambience, and many of the quests were really memorable. Oblivion felt more challenging, too. Plus the Imperial City was really and truly staggering in size, much grander than any city found in Skyrim, even if its inhabitants did keep spouting the same inane nonsense in the vein of "I just saw a mudcrab the other day".. "ahem ,yes!". Hehe, that reminds me of a moment in Oblivion that almost made me choke with laughter: the innkeeper of Luther Broad's Boarding House (at least I think that was the place) in the Imperial City was talking to his servant. The dialogue went like this: (luther): "Whenever I have guests who visit the Imperial City overnight, I direct them to the King and Queen Tavern". (servant): "that's the only sensible thing to do, really". =DD I guess Mr. Broad didn't want any customers!
Anyways, one could also argue the land of Oblivion was more diverse than Skyrim, with subtropical swamps, temperate forests, rolling hill-lands, grassy highlands and snowy mountains, not to mention the hellish dimensions of Oblivion. Skyrim on the other hand has a million varieties and degrees of cold, but it's rather limited thematically. Whether that's a good thing or bad thing depends on your preferences.