Also you'll forever be haunted by the knowledge that you took the easy way out.
OR: if you're a role-playing type like myself, you might be haunted by the fact that you essentially stole someone's body for the Adra dragon to escape with, and that by all accounts the Adra dragon was a fairly unpleasant individual to release upon the world (assuming you are role-playing a relatively good character).
I disagree, both as a role-player and as a "user". The Endless Paths of Od Nua are designed with character levels 5-9 in mind. Except for the Adra Dragon, everything goes down smoothly. This, plus the fact that the dragon's quest gives you significantly more XP than just killing her makes me fairly certain that this 'easy way out' was the "recommended" way to finish the Paths. The adra scales are cool, but you get countless Superb quality equipment throughout the game, so its really nothing groundbreaking - no offense.
As for the role-player part: The adra dragon doesn't seem evil. She tells the player outright why she doesn't want them to leave. She also tells the player about her life and how she holds everything she saw dear to her. She also doesn't seem to have any evil intentions once she is in a mortal, human body. And I'm saying this as a very Benevolent player. It's also cool as hell to have a dragon be indebted to you.