Oh yes. You are right, I was waiting (and not only I) for being able to play on the dark side of the Force but not like in SW games before - side-quests or couple of dark side choices but as a Sith from A to Z in fully immersive story. For that BioWare has my respect (and EA has my $).
I don't know if it is true in all cases, but I feel that Imperial characters are more mature-written then Republic one. I'm very curious about late-game Republic story, because as my predecessors said it shows the corruption and rottenness hidden under the mask of justice and democracy of Republic itself.
PS: I have noticed (and I believe it's not so subjective as it would look like) that there are quite significant, if not huge, differences in the quality of class stories.