Well, why don't I just clear the whole thing up...
Dark Forces: Early Lucasarts first-person shooter (shortly after Doom) in which you played Mercenary Kyle Katarn, working for the Rebel Alliance shortly after ANH. Quality in many places, but criticised for being repetitive, too tough, and for not having lightsabres! No multi-player either.
Dark Forces II: Jedi Knight. Done a few years later, post-Quake, and so using a 3d engine, that was not too bad. You play Kyle Katarn again; responding to criticism, they take the welcome (though, plot-wise, rather ludicrous) step of turning him into a Jedi Knight, where he becomes the most powerful Jedi seen (from nowhere) within the space of about three days... improbable Force Powers and a wide variety of Dark Jedi prevail in this post-ROTJ game. Very silly but VERY fun. The sabre was cool but not cool enough; you never seemed as dangerous as a Jedi should be and the duels were pretty rubbish. You could also turn to the Dark Side in it, in which case you got a MUCH cooler ending. But the Dark Side fireballs took the piss.
DF II: Mysteries of the Sith. The expansion pack for Jedi Knight, having you play at first Kyle Katarn and later Mara Jade, having introduced the plot of her learning from him after Luke. You could only be good in MOTS, sadly. Good quality but, in the end, more of the same. Very Star Wars-esque ending, though.
Dark Forces: Obi-Wan- At first called Dark Forces III, they removed the 'III' tag (because it wasn't really a sequel to II), and it looked like 'Dark Forces' would become an umbrella term for all first-person shooters based on Star Wars on the PC.
Obi-Wan boasted many new and exciting features- the 'rune' based sabre fighting system, that promised simple yet skilled sabre fighting, analogue force powers (e.g.- using force push on a pot, you could push it gently so it just swayed, push it HUGELY so it flew away and shattered, or push it just enough so it fell off the window sill and onto the guards head), and of course the opporunity to play the man himself, Obi-Wan
Until Lucasarts got a new President. He took a long look at the game, and declared three things- a. it wasn't really a Dark Forces game, b. it's arcade style was more suited to consoles than PCs, and c. it was RUBBISH!
The whole PC project was canned, the Dark Forces title dropped, and the whole thing re-worked into a simpler console action game witb many of the features dropped. So we'll see how good it is soon.
Dark Forces III- Jedi Outcast. Much of the PC Star Wars playing community felt like communal suicide when Obi-Wan was pulled off the PC. The fact that it had been no good all along only made things worse. Fortunately, Lucasarts had no intention of giving up the Dark Forces tag-line- especially not while they were sales to be made.
FOllowing a new policy of contracting out their games, they asked veteran first-person shooter developers Raven to make a new game for them. This was eventually settled oin as a true sequel to DF II. Jedi Outcast has you playing Kyle again, who has given up his sabre and his force powers and become a boit of a hermit. This, of course, gives an excuse for you to start from scratch in getting your powers back, and even a more credsible reason as to why you get them so quickly- you are just remembering them. Still a bit dodgy how you got them in the first place...
Even MORE Dark Jedi abound (must be thousands if the buggers), whom you will presumably hack to death. Force powers are stil, a little over the top but apparently not quite as silly as DF II. Sadly, it seems they have made no effort to improve the sabre fighting, other than some (admittedly welcome) work on making the duels LOOK better- flips, fast storkes and all (sabre strokes were always FAR too slow in the earlier game!).
I think developing a skilled but practical sabre system is proving impossible for now. So DF III is playing it safe, so as before, it will probably be a bit silly but great fun.