I just finished the main story for Dark Forces II. I had a little bit of help with the final boss, in the form of an invincibility cheat, but that's only because light saber combat in this game is a mess. The controls are so sloppy that I couldn't really develop a skilled technique. I wound up just flailing around randomly in the hopes of landing a decisive hit. As a result, it didn't really feel like I was giving up when I skipped the real fight.
Anyway, about the story. Kyle Katarn's father was a Jedi (despite the fact that the game is set after the third movie, which would put him in the same age bracket as all those Jedi Darth Vader was supposed to kill) and he had a mysterious artifact that, when combined with a certain map will lead to a location called "The Valley of the Jedi." At the start of the game, a dark Jedi by the name of Jarec kills Kyle's father in the hopes of gaining the information necessary to go to the Valley and claim its awesome power for his own. Obviously, Kyle wants to stop him, but is constantly one step behind and thus doesn't get to confront Jarec until his plan is, like, 99% complete.
The plot's biggest strength is that it has that classic pulp feel. It's a race to uncover an ancient archeological mystery with a dashing hero and a thoroughly loathsome villain who makes the mistake of making things personal. It's not a story that holds many surprises, but it's perfectly serviceable.
The biggest weakness of the story is that it sometimes feels like it's trying to one-up the movies. Kyle Katarn is a Han Solo-esque rogue and also has Jedi powers. There's more magic, the stakes are higher, and the villains are more depraved. As much as I would have hated to miss out on the magic powers, I think the story would have worked better if it had the confidence to a low-key story and Kyle Katarn would have worked better as a clever, but mundane mercenary.
I still have another seven hours to play the game. I don't think there's anything left in the story for me to uncover - it's as straightforward as it gets. However, there's still a lot of secret areas and the Dark Side powers and medium difficulty. I'm going to try for a 100% completion, though there's obviously not enough to do it. It's just a thing I have to do.