The Standard of future RPGs.
Then the DCL and player created downloads added to what future games should encompass. Pets, other realms, and finishers being among them. The game had over 100 quests, used almost every item at one point, a leveling system that made since and allowed you to feel stronger. And even though the quests with choices were limited the did present a good guy or bad guy feel which bethesda continued in their next project Fallout 3.
People who have played Oblivion won't except games without the concepts embodied within it and bethesda should be proud. Thus Elder Scrolls is a great representation of the growth in RPGs in 3D.