This game is about as open ended as it gets!
You can join theif guildes or fighter guildes or whatever you want and work your way up the ranks, like in Baldurs Gate 2 but much more to it.
The best part is that there is NO RANDOM DUNGEONS like some mindless action games (Diablo) so when you go in a dungeon it really feels like you are there. The artists placed everything right where you see it. Walk into a bar or something and there are tons of hand placed objects decorating the place, its really cool.
The Equipment/armor system works WYSISYG so if you find a cool new helmet and put it on right away your character will show it, even down to cheap pants vrs expensive pants, ect.,
This game feels like a MMORPG only single player, and obviously much more interactive, for example finding quests is easier, much more streamlined.