I must admit, I haven't played each of the Mass Effect games more than twice, and both times I've played as Paragon, so I have as much idea about the difference as a person who's read about it on the game's Wikia. Moreover, I've never replayed RPGs with different morality because I don't get the kick from it. I've never played Baldur's Gate and I barely touched Torment: Planscape.
Perhaps, you're right to say that Mass Effect is not on the level when it comes to dialogue affecting the world. Maybe it wasn't designed as such. Maybe it was designed to tell a story which has more rails than, say, Baldur's Gate. Maybe it was designed to tell a story, closer to a book than to free-roam RPGs. As such, it succeeded, and as such, I appreciate it. Don't judge it by what it's not: it will never become it.
That being said, have you tried Arcanum or Pillars of Eternity? Those are the kind of games you might very well enjoy.