This is more the game PSP owners have been waiting for than FF VII fans.
Now, if you already do own a PSP, there's almost no reason not to pick up Crisis Core, it's one of those games you need to own to help justify the system itself. I don't really have to touch much on the story for those of you who have played FF VII, it covers a lot of ground you already know, and hits on a lot of new areas that you don't. And, even better than providing a lot of answers, it just opens up new areas for debate. One of the best things it does, is never feel tacked on, the story flows fluidly and naturally, and feels like a proper prequel to the series rather than a cash in mess.
People who haven't played FF VII, I'd still reccomend the game to, as a competent Action game, but if you have been thinking of picking up an old copy of FF VII to play I might reccomend going through the classic RPG first, so as not to ruin a few of the more interesting plot points that the game somewhat assumes you already know. (Then again, if you've already had a lot of the plot for you ruined by reading through hype, go ahead and pick it up.)
The gameplay is solid, if somewhat easy in the beginning. The game does a good job of keeping you somewhat restricted during battle (Zack autofaces when he attacks and will always close distance with an enemy before swinging), which works actually quite well given the portable system it's on, keeping you from having to worry about fighting camera angle or the sometimes unruly thumbstick. The ammount of customization you have available to you with materia works out very well, and you'll often find yourself swapping them and your equipment to match up to the types of enemies that you're facing, which is the mark of a good customizing system.
The missions are were the real meat of the difficulty in the game lies, and also what helps to make it portable friendly. The main storyline is well told and often is broken up by well executed minigames, but chapters can take a little while to complete. Missions move faster but have nothing but straight combat. Still, while the game for the most part can be autopiloted pretty easy with standard hack slash victory, the later missions start to throw more and more dangerous enemies at you that can really test your timing and reflexes.
The graphics are absolutely amazing for the PSP, both in the CGI cutscenes and everything that happens in game (anyone playing will notice a distinct similiarity in character modeling between it and the team that developed Kingdom Hearts II, making many of the characters expressive, but not always as dark as you might have expected.) The music is well scored, but most of the new tracks aren't as memorable as the returns to the classic score that show up.
It's a game that is suprisingly hard to put down when you pick it up, and is never shy of challenges to complete, or of story that compels you to go in deeper. If you have a PSP already there's no reason to miss out, and if you've been thinking about buying one, this is certainly a time to consider it.