Have you played
Divine Divinity? It's more action-y, but it has a very expansive world and I thought it had a really good element of character building to it. There's a sequel
Beyond Divinity that I think had a better character creation system, but I didn't much care for compared to the first. There's another game in the series
Divinity II that is a bit more 'modern' in how it plays, but is a fun game all the same.
Also, if you're looking for something more along the pen and paper lines,
Temple of Elemental Evil is pretty good once all of the community patches and updates have been applied to it. The big fix/mod pack for it is by Circle of Eight and can be found
here.
If you don't mind graphics, the
Avernum games by Spiderweb Software are excellent and they all feature open worlds with fairly decent character building. The stories to them are pretty fair, as well.
Along the lines of Avernum are the Eschalon games (
Book 1, and
Book 2). They're single character games, but they feature solid character building and pretty good stories, as well. There's a third game in the series that is expected out sometime this year. I've played the second game in the series and I consider it one of the better RPGs I've played in recent memory. If you're interested in seeing how it plays just poke around on YouTube and I'm sure you'll run into my blind LP of the game and you can see how it runs.
There are some older series that are more 'classic' in how they play like Might & Magic or Wizardry, but I think they might be a bit
too archaic unless you don't mind games where the majority of time is spent cutting through hordes of enemies.