If you can deal with the dated character models (environments look fine IMO), lack of a functioning third person camera, horrible leveling system, and not-as-good mechanics in combat and lack of a perk system, Oblivion's gameplay, story, quests, environment, voice overs, etc are all fantastic. There's a lot of mods for the game, so a lot of those problems can even be fixed in the PC version. I'd get the game of the year addition, because the DLC questlines are all pretty fun, but the Shivering Isles is EPIC and really deserves attention.
All in all it's a great game. A little dated, with a very bad levelling system (you can actually get weaker by leveling up, which is ridiculous). I might actually reinstall it with mods because I'm getting a little bored playing skyrim too much