Not quite as great as it could have been, but there is plenty to like about the Force Unleashed
The story takes place in between Episode III (Revenge of the Sith) and Episode IV (A New Hope). Darth Vader hunts a jedi on the Wookie homeworld, Kashyyke, and he discovers that the jedi had a son. He takes the boy (who he calls Starkiller) away with him and for the next couple of years, trains him to become his "secret apprentice" so he can take down the Emperor (I won't spoil anymore than that). The story in this game is actually one of the best Star Wars stories in years and the voice acting is quite good as well.
For the gameplay, of course, as a jedi you run from one end of the level to the other and kill storm troopers (and many other creatures) with your lightsaber and the force. When you kill an enemy, you earn a little bit of experience and eventually, level up. You get points toward your force powers divided into 3 categories (power, talent, and combos). Power upgrades your basic force powers like lightning or grip, talent helps your status like more maximum health or more saber damage, and combos gives you, well, combos (push buttons in a certain order). Also, this game is actually quite hard. I even had trouble in normal (sith warrior).
You start out with a red light saber but throughout the game, you can find crystals that change the color to blue, green, purple, orange (it says "gold" but it looks more orange), etc. as well as your costume.
The graphics are pretty good but the physics are incredible, some of the best I've ever seen. Wood breaks like real wood, glass breaks like real glass, and even the stormtroopers (or whatever) react well.
There are a few glitches and there are other things that annoyed me (like the load times) but The Force Unleashed is a great addition to the Star Wars saga and a great game all around. If you like Star Wars or just like action games all around, then this game is for you.