I've said for years Adel was wasted.
The flashbacks with Laguna really set the tone and it's only made more awesome when everyone is flipping out about her being released. It gives you great insight into how truly frightening she is.

Also, the whole "well Adel might actually beat Ultimecia" was great too. It made you appreciate how powerful she was if it was theoretically possible she'd defeat the main villain.

Finally, the fact Adel was never fought at her best but in a weakened state kinda makes you think she's damn near invincible as the game had ot handicap her before the heroes could win.

Oh and we can't forget Ellone giving that little line about being inside the mind of a young Adel. It makes you wonder what it was like. I'm guessing it was rather tragic and I wish it had been explained.