Basically as was previously said, I like the Avernum series for the open-endedness and that you can in a sense "create your own adventure," as cheesy as it sounds. For me, I never got into the Geneforge series becuase there, from my experience, isn't as much you can do and explore, while it basically retains the same style of combat as all of the other games.
-Spartacus, who find it too tedious to type out signatures like this to do it any more after this, just made his first post on this forum.
EDIT: Just to add something, which you will probably shoot me for, I have never really paid attention to much of the storyline in any of the games.