It's just a great game.
Graphics: Spectacular. One of the best looking PSP games to date. This game really pushes the system.
Gameplay: A button masher with a command box is basically what it is. The special moves in the game are random and isn't explained very well, something that has to do with the main characters memories.
The battle system is all real time, unlike other Final Fantasy titles.But it has this simplicity to it that somehow makes it perfect for a portable game.
Story: Basically the best part of the game. It tells the story of Zack, and his adventures leading up to Sephiroth going crazy and Zacks inevitable death.
Characters: Returning-Cloud makes an appearance and so does tifa. Sephiroth is obviously a big part of the story.
New: Zack (although he was known in the original FF7), Angeal(Zacks mentor that has honor on the brain), and then Genisis, whom you can think of as the bad guy in FF7 before Sephiroth.