Don't listen to all the hype, it's not the Holy Grail of Gaming. That being sad, it's a lot of fun.
What this game is though, is the Half Life 2 of roleplaying games.
Exceptional presentation, both the visuals and the sounds are stunning. Add to that an absolute insane attention to detail in both visuals, but also gameplay and story, and you are left with one of the most immersive gaming experiences out there. Oblivion definite puts YOU in the game.
I'm not a big RPG fan, as I tend to like the action a bit more, and this game seems to be the perfect balance. All the RPG dressings of leveling up, gaining skills, getting more powerfull as the game progresses, are there, but the action really is left up to you the player as it's your deeds, not your characters stats, that determine the winner of battles.
Tons of Fun, Interesting things to do, and lots of different ways to play the game. It's a game that should keep you interested for quite some time.