'Dialogues' become boring when they're freaking monologues. It has to be interactive in more ways than just 'go on, please, please just go on' virtually all the time. Dialogue has to feature a gameplay element, in which the player actively interacts and plays a part in said dialogue, not just be an exposition device. The conversation with Atris (I timed it! 45 mins!) is one of my favorite scenes because it WASN'T a monologue. You were defining your character at the same time as being fed relatively large amounts of information about your past. Would it have been more fun if it were full of narrative such as 'Atris leans back and strokes her chin, her icy glare piercing your eyes with hot sweaty hatred'? I'm not convinced.
MCA isn't wrong, though. Economy of words is important. Be too overly verbose, and the player isn't even reading what you're writing. In which case, you've already lost.
The thing, all that energy being spent on narrative and descriptions I would rather have invested into further character development and relationships, especially with party members. The amount of input those dudes get during dialogue is very appreciated, but please sir, I want some more. There's a lot of room for more interaction there. This was done much better in KOTOR2 than in PST, in which, intraparty interaction was pretty minimal - it was basically 'you and me' relationships. I'd give up narrative for this, especially when ample narrative isn't really that optimal an option anymore.