I played through Oblivion again 2 months ago. Actually, I ignored the main quest this time because, for me, the main quest was complete bull crap. I hated it, I hated the endless oblivion gates, I hated how they spawned everywhere. It just ruined the world. I dunno. I just kept this amulet of kings for myself. Screw these guys.
It's hard to say if Fallout 3 is better... Probably is... I really think I had more fun exploring the Fallout 3 world. It felt more alive, even though it was desolate. Hard to explain why. It's the same for Morrowind, the predecessor to Oblivion. I preferred the Morrowind world because it was more focused. It had its distinct feel. Oblivion was just a mashup of fantasy world settings... oooh snowy mountains... ooooh swamps... ooooh forest... All cramped together.
One of Fallout 3's short comings was the lack of a reason to come back to certain towns once you had been there once. I mean, you complete the quests in Megaton, and that's it. Every one has his one quest and nothing new apparently shows up after that. Another short coming was the level cap and how easy the game sort of was, it gave you too many points, I dunno, it seemed like you could basically specialize in so many skills. Definitely should have stuck to a more stingy and difficult system like those of Fallout 1 and 2. The perks system was nice...
I rate Fallout 3 pretty highly. I played it obsessively until I finished it, and then I went on an exploration rampage. I played way over 50 hours, probably closer to 100. I may go back since I had started a new evil character.
I liked Fallout 3 and Morrowind about equally. Liked them both more than Oblivion, which is still a decent game. I mean, I did play Oblivion for a lot of hours too. There were just too many random ******** things related to levelling (levelling up should always be a good thing...), and the contrived world as I mentioned, and the ARGH main quest... It had to be modded to be enjoyable for me. Not the case for Morrowind and F3.