This is the game the really started it all!
Dark Forces was a great FPS back in 1995, I upgraded my computer just to play it. It blew Doom, Duke, and Heretic away. But in 1997, Jedi Knight was released, and yes, you could now swing a lightsaber. And, it used a full 3D environment with acceleration.
On the surface, it was like any other FPS, only now, you got a lightsaber. Lightsaber combat by today's standards (8 and a half years later), was very simple. But then, you had three basic types of attacks. Your primary, standing still attack had a full range and light damage. Your primary, while moving, had a condensed range with light damage. Or, you could "Z" attack and do quad-damage with two swings (only one swing can hit though, if the first hits, the second misses).
The single player game was good, but it was the multiplayer aspect, the thought of real Jedi dueling real Jedi, that spawned thousands of JK clans all over the internet. And I still play, every week. ^_^