Makes you not want to put it down...at times.
The plot can totally engulf you, and keep you thinking until the very end. Just when you think you have it all figured out, something else happens so you feel like an idiot for thinking what you did. But the fact that it kept you guessing isn't the best part of it. It was the plot itself. With a terrific plot, and an excellent way of telling it, you can't help but love this game.
Any good game HAS to have good characters. Characters that make you root for them, feel for them, really care about what happens to them. I think Star Ocean does this. From the very start, the game makes you really wonder what happened to Fayt's dad, and hope that he is still alive. All throughout the game, the characters make you feel about them, and a few make you wonder how they came to be tangled up in this story.
I think I played certain parts of this game for hours upon hours at a time, either wondering what's going to come next, or leveling up, or mastering your skills you gain when leveling. The Battle Arena is a great example of this. When I found a fun fight or a fight that will you a lot of experience or a lot of Fol, you wanted to just fight that team or rank over and over and over again.
One bad thing about this game is how pointless some of the game seems at times. Almost the entire time you're on Elicoor has nothing to do with the main storyline, except showing the power of Fayt at the very end, and also to show you the location of a couple of dugeons later on.
Weighing the good with the bad, I would highly recommend this game.