The Force is fun to play with, but the story hurts the saga more than it helps, its fun but too short.
The premise to the Force Unleashed is that you play as a secret apprentice to Darth Vader, found at the end of the opening level where you actually get to play as Vader himself, while on a mission on Kashyyyk, the Wookie home world. From there, you play as the secret apprentice, going on missions for Vader, hunting down any remaining Jedi in the aftermath of the Clone Wars. The story continues on from there, bridging the gap between Episodes III & IV. It is an entertaining story, however it does lead to some issues with how the original Star Wars trilogy is now perceived based on the events of TFU.
The gameplay is your standard third person action game, most comparable to Heavenly Sword in my opinion, in a lot of ways too. There is a soft lock on feature for the apprentice's force powers, like force grip and force lightning. Movement is standard to the left analog stick with camera control on the right, incidentally the camera can be rough at times. Jumping is mapped to the X button, [] attacks with his lightsaber, Triangle is the Force Lightning button, O uses Force Push, R2 is Force Grip, L1 performs a Force Dash, R1 is a lock on and L2 blocks. The controls are good, although the lightsaber attacks felt weaker than your force abilities. However that can be augmented as there is a light RPG leveling system in the game. For every level you earn 3 force points, one for force powers, one for force talents, and one for force combos. Combos unlocks more lightsaber combos obviously, powers unlocks or strengthens your force powers, and talents strengthens the apprentice (more health, force points, etc). As you play you can also find lightsaber crystals to change the color of your lightsaber plus crystals that provide some bonuses, like a higher blaster deflection rate or life steal.
The levels are pretty straight forward, though there are some hidden areas. There isn't much story during the levels, although there is some dialogue, otherwise there are cutscenes that start and end the level. For the way the story is hyped as an official bridge between the trilogies, there could have been more scenes to help the story to develop some more. Even still, there is a fair amount of dialog during the levels that help keep the story moving.
The graphics are very nice, showing off a number of planets from the Star Wars galaxy. The characters, planets, environments, not to mention the force powers, all look very nice and fit in. Enemies are pretty generic, aside from the bosses you encounter and the Jedi you fight. The big time characters from the prequel trilogy look very nice, and are voiced well, even if Jimmy Smits is the only one to reprise his role, as Senator Bail Organa. Audio wise TFU is just like all over Star Wars games, it sounds great. You'll hear the same familiar themes from the Star Wars saga.
There are a few missteps with TFU. First off the game is too short, especially since the story is considered canon as the bridge between Episodes III & IV. I finished the game in under 6 hours. And considering you revisit three worlds, TFU just doesn't feel like it was developed enough. Also, as I mentioned once before, while the story is good, it does tarnish the glorious image of the original Star Wars trilogy. The events of TFU help setup the original Star Wars trilogy? Seems like the more the Star Wars saga is developed, the worse it gets. Getting away from that, the gameplay can be fun, but there are enough times where its not, particularly in areas where you have to fight multiple types of enemies who all have different methods to defeat them. And this is bad b/c most of these enemies have power weapons that can knock the apprentice down allowing other enemies free damage. That's irritating.
I was somewhat disappointed with Star Wars: The Force Unleashed. The best game I can compare it with is Heavenly Sword, which also featured a good story, good gameplay but was short as well. What hurts here is that the gameplay is worse in a few areas, there's no huge mega battle that HS has near the end, and the story really does hurt the Star Wars trilogy more than it helps it. Still there is fun gameplay to be had, despite my criticism. Unleashing the force hasn't been this fun, but due to the length, I'd recommend renting as opposed to a full purchase, unless you find it cheap.