I take issue with that. Exploration in Fallout 3 was terrible. Oblivion had variety, it had different climates, it had more elevations, it had more cities and towns and you could explore every ruin and cave which dotted the entire map. Fallout 3 was just flat and muddy and boring. Everything was the same palette. Everything was the same texture. Everything was the same model. You couldn't explore most ruins, there were few places to go, there was nothing to do. I thought all this boring brown crap died with Quake 1.
Fallout 1 and 2 and FO Tactics were not boring nor repetitive because how the 2D world was drawn and how structures and maps were created. Bethesda took a great franchise and made it the most repetitive and uncreative sandbox FPS I have ever seen.
Stalker is what you really should be looking at if you want to see a well done and immersive RPG like sandbox post-apocalyptic FPS world that is not repetitive and always engrossing.
Oblivion had the same few textures repeated a few million times. Though FO3 did as well, but something about the look of it was more interesting then the bland, generic, lifeless feeling, a-typical fantasy world of Oblivion.