Did you even play Oblivion? The different parts of the map all had their own style. Bruma+the North was snowy, pine trees, Nord architecture, higher altitude. Bravil+Leyawin were swampy and had more of a cheap shack architecture with corresponding swampy flora, Cheydinhal+the East were very dense style forests and had Dark Elf architecture and that's not to mention the rest of the areas which looked distinct. You could show me a picture of any landscape in Oblivion and I'd be easily able to tell you in what area you are.
Anyone who says all of Oblivion looked the same either never played the game for more than a few hours or is straight up lying.