Love them both, but for different reasons. Fallout is very impressive, but feels somewhat "smaller" because it has less quests, no real factions to work for and a finite storyline that ends at some point (lest you buy an expansion). I love Oblivion 'cause it has a ton more stuff, but as I said I love both games. Only thing I don't like about Fallout are the expansions or DLCs, since apart from Broken Steel they're pretty much standalone 5-10 hour "single adventures", and I don't like that. I prefer stuff that integrates into the premade world.