RPGs that are on the PC are mostly of the WRPG (Western) variety. WRPGs tend to be more open ended than JRPGs (Japanese), which you find a lot of on platforms like GBA, DS and PS2.
From my experience, I'd say that JRPGs are more story based, where you follow a more linear path. In the case of WRPGs, you have a more open ended quest, where you have a greater amount of control of how your character reacts to different situations and you have more flexibility in the progression of the story. You also get to further customize your character, including their personality.