You don't need PST level writing quality to have an enjoyable RPG. Back then, when we pushed pixels through IE landscapes, there was kinda nothing else to do than reading, messing around in inventories, and killing stuff. So you sorta had to deploy a Gaider or an Avellone to keep us entertained.
Witcher succeeded on many levels, gameplay wise. The combat system was imo a vast imporvement over Kotor, NWN2 etc. The setting was well developed, the characters ranged from awful bad to interesting and multilayered. There was lots of stuff to do, and lot of choices to make. Overall, TW did more things right than wrong. And that's kinda a little miracle these days were we get polluted with wannabe Action RPGs that always seem to be either an Oblivion or a Diablo clone.
Edit: Stupid typos, shouldn't drink so much wine...