The first time the developers were really able to spread their wings and try something new, despite being reductively written off as "Oblivion with guns", Fallout 3 was a huge departure for Bethesda.
Maintaining the same engrossing quest structure and ostensibly the same rhythm of Oblivion, Fallout 3 felt much better to play thanks to the variety of enemies, the ridiculously gory combat and the ability to genuinely live and survive in this dangerous post-apocalyptic landscape.
Likewise, although The Elder Scrolls is a series full of distinct worlds with their own sense of place, neither the snowy mountain villages of Skyrim nor the urban areas of the Imperial City hold a candle to the character and personality found in the ironically desolate wastelands of Fallout 3.
Just hearing the opening bars of "I Don't Want to Set the World on Fire" by the Ink Spots is enough to transport players back to the first time they booted the game up. Fallout 3 was a genuine phenomenon, and although it may not be the most technically polished or consistent game Bethesda have released, it's the one that by far left the biggest impression.