I first played this on the 360 before getting it on Steam and I've pretty much done everything on it so here's an overview.
You're name is Starkiller and you're Darth Vader's secret apprentice, oooh exciting stuff.
You go out doing his bidding which involves hunting down the remaning Jedi hidden across the galaxy and other missions without ruining the plot.
You're armed with your trusty lightsaber and forcepowers which can be upgraded as you progress through the game.
Lightsaber colour, beam, force strength, force lightning strength etc. Some of the lightsaber crystals have their own perks you can chose from, faster force regain, more health etc.
You also unlock costumes, so you can look like a true Jedi or a sith warrior, your choice.
In terms of combat, you again unlock combo moves which are handy as you encouter difficult enemies later in the game.
Or just throw a Stormtroopers at each other, or a tie fighter, force push them into oblivion, slam them against a wall until they black out, you decide.
But my main gripe with the combat is the fact that your lightsaber seems to be made out of plastic, I mean seriously, you can hack away at a Stormtrooper relentlessly and he'll still be in tact. Makes no sense to me considering in the movies everyone decides they don't want their hands anymore when they hold a lightsaber.
You may think it's minor, but it puts me on the verge of tears. I want to slice their heads off, cut them in two, send more hands everywhere while I announce I am their father. Weird thing is you can impale them with your lightsaber, but not cut them up.
What I also will say is that, once you complete the game you will be hit with a severe lack of replayabilty. I guess it depends if you really love the game.
The Steam version from what I can tell from has none of the achievements on, so you can do the harder difficulties for some nice costumes but that's it. No virtual achievement to show that you're a virtual badass on a videogame, making me tear up again.
Well that's my opinion on the game, oh and for the record, don't get the second game it's abysmal compared to this one.