So, here are some unstructured thoughts on Crisis Core:
I love what this game did in regards to the Nibelheim incident. Playing through that as Zack, fighting Sephiroth, being captured by Hojo and escaping was probably my favourite part of the game.
Seeing Zack and Aerith was nice too. Him asking her for a date, giving her the bow and giving her the idea to sell her flowers were all great moments.
I didn't like Genesis. At all.
Angeal was a character who I actually kinda liked, serving as "Zack's Zack" as someone here put it. He serves as a strong emotional motivator for Zack, and feels necessary.
Seeing "good guy" Sephiroth was cool, and the simulation battle was enjoyable. Very AC.
The ending was powerful, with Cloud's yell actually making me jump, lol. Zack achieved his dream, finding the satisfaction that he thought he'd get from becoming 1st class (I think he was grinning when he passed away). As it rained upon the sector 5 slums (is there not an upper sector 5 plate?) Aerith sensed Zack's death, leading into a pretty cool cut back to Zack. Cloud takes the buster sword, and finds his way to Midgar.
I got really bored of the missions. After a whlie, you realise that you're essentially just doing the same thing over and over again.
I feel like the vast majority of Crisis Core's strengths come from the FF7 callbacks.