Open world RPGs were always the goal, old games tried to mask the hardware limitations by using several techniques. By the time the Witcher 3 came along open world RPGs were the most common thing, in fact at the time lots of people called the Witcher a sellout because of that, it's like if it had come up a couple years ago and had base buildiechanics, EVERYONE else was doing it.

There are LOTS of examples that pre-date TW3, I'll limit myself to a few, just because it's the ones I played. In the 90s and early 2000s I used to play Ultima Online, which is an MMO from 97 that has a vast open world. But if you want first person, Oblivion is old enough to drink.