One thing I hated about VIII was how you could miss out on Aeons, Eidolens, Espers or whatever the fuck they were called in that game (Guardians I'm thinking maybe?). Since a lot of them had to be drawn from your opponent during a boss battle you could miss them. They offered a chance to get them again but it wasn't until you finished 99% of the game and were at a point of no return. On my second playthrough I missed an early one and didn't realize it until much later and I wasn't about to restart at that point. I want to say Carbuncle.
The first time I played the game, it was OK but I beat it out of a sense of duty to the franchise. It was, by far, my least favorite game in the series though especially after VII. I didn't figure out the enemy leveling system until later and I made the game unnecessarily hard. When I got to the end I barely beat the final boss and was more relieved than anything. I gave it a second chance years later and it was a better game that time since I understood some of the weird rules better. But I still think it was a weak entry into the series. I maintain that Square knew they had struck gold with VII and they simply went different for the sake of being different.