Yeah, the Knight's story is pretty much what KotOR 3 would have been. It's the most traditional and epic "save the galaxy" type of story...which to me makes it a bit dull because it doesn't really bring anything new to the table, but it's decent.
The rest of the stories are really just a matter of what you're looking for. I personally think the IA is the best, but there are several who would disagree. The Consular is alright, but it's a slower-paced story more about building alliances than saving the galaxy. The SW story is pretty good, but I thought the SI story was dull until Act 3. The Smuggler and BH stories are enjoyable, but they're much more character-dependent than the others. You're basically looking out for your character rather than saving others, but they have some of the best companions and dialog so to me they're worth playing. And the Trooper is probably the best look at the regular, day-to-day operations of the Republic.
Thank you very much. Before I start my Agent I would just like one person to give a decent response about the Warrior.