While it's true that the cutscenes do not tell a complete story, that didn't detract from my enjoyment. The cutscenes themselves look amazing. If this is the animation style that will be used in the upcoming Clone Wars TV series, sign me up!
BTW, I liked Zam's character a lot more in this game than in Episode II

If you really want the full story, it looks like there are a series of movie files in the DVD-ROM content that show cutscenes AND gameplay (though I haven't watched them all, or even made a dent in the DVD-ROM material).
Thanks to Galactus and MoveAlong for a great disc!