Republic Commando is X enhanced, but I find it a bit plodding. Jedi Knight (Dark Forces 2) for me.
Agreed. Jedi Knight is great.
Dark Forces 1 is just an okay Doom clone. Jedi Knight II, I found to be a bit of a slog. But Jedi Knight was fun all the way through.
Bonus points to this series, though, for inventing the wacky sequel-naming tradition.