In my opinion the best part of oblivion was exploring around. I didnt like the story, or the combat system and i would much rather ignore all oblivion gates because their content didnt appeal to me...
BUT
What I enjoyed a lot about oblivion (and more so than in fallout 3) was just exploring the world. It is a very beautiful craftmanship and it is very immersive just walking around and listening to Jeremy Soule... Almost Zen. (I think my point is that might enjoy just wandering around listening to dark music)
Fallout 3