Well, Deus Ex and JK2 are my two favorite FPS games, so I guess a combination of the two would be my ideal FPS. Deus Ex was great in terms of character interaction, plot, and player customization, but the actual combat in the game was "flat" at best. It would be awesome to have a Star Wars game with a plot other than "kill the Imperial splinter faction" or "kill the pirates," where the characters came alive and had their own agenda, where your choices as a character affected your relationships and the world around you...with the intense lightsaber combat as a bonus. But what are the odds of that happening?
Also, TIE Fighter is by far the best of the old LucasArts games and does deserve a sequel. X-Wing Alliance was okay, but the plot never really got me involved at all. It would be great if they implemented a system where you could work your way up through the ranks, eventually being able to control Imperial fleet movements, deciding what to send into battle, etc...of course, I would be more than happy if they just re-made the old gameplay in a brand new engine. Of course, LucasArts would never think that making a new game about Imperials is "commercially viable," even though TIE Fighter enjoyed tremendous success.