Really. The darkside ending is just like BAM! IN YOUR FACE! OMG YOU JUST GOT TOTALLY OWNED BY AN EVIL CLONE OF YOURSELF! FROM BEHIND! AND THE GIRL YOU WENT THROUGH ALL THIS FOR DIES! EPIC FAIL!
Lightside ending is like Awww... that's sweet. The girl lives and you finally ends up being able to be with her. The universe is at peace and Vader is captured. Or so everyone thinks... ENTER BOBA FETT!!! *badass commando music, blaster noises, rocket launchers, people dying, lasers, lightsabers, EXPLOSIONS!!!* Fett. Boba Fett.
Only that last part wasn't in the game. If it had been then yeah... lightside would have completely kicked darkside's ass.