Syrion: That does indeed sound a like sensible choice of a mod to use in my case.
I take it you mean the "LOD (level of detail) texture/model fixes" as mentioned by mwnn here? Although, I must say that I was surprised by how bad the game looks, even for the time and artistically, especially on level 3. So, I'm not sure it really changes that much for me, hehe. But, I'll give it a try, thanks for the recommendation!
No, I didn't use the "LOD" fix, since the guy says in the post that it caused issues (and he'd already removed the links, anyways).
What I'm referring to is the "Jedi Knight Retexture Pack". You can download it
here. Just to be clear, there
are some custom textures in it, but it seemed to me (in going back and forth, comparing the first level with and without the mod) that the game looked the same (and how it was meant to look), just better.
There's also the "Jedi Knight Enhanced" mod (available
here under JK_Enhanced.zip), which replaces the enemy, NPC, weapon, item and player models with higher-polygon versions, along with higher-quality textures for them. Most of the models and textures are taken from Jedi Knight II, so they're authentic to the Jedi Knight series, just not to this iteration. In other words, enemies, NPCs, weapons, items and the player will look like they do in Jedi Knight II. That might be too much of a change for some people, but other people might not mind, since they're just coming from the sequel, not from a 3rd party.
Those two mods are, I think, the two major ones that most people try out first.
BTW, I can also vouch for the improved music replacement. It's exactly the same music tracks, playing at exactly the same times in the game, just in noticeably better quality.