There were videos and posts relating to the fact the GeForce 3 and 4 used some kind of buffer for the shadows and modern cards do not have this so the shadow/lighting is not working properly like it was in the original xbox.

Has this been fixed? I know there were ini tweaks to force it on but that was buggy.

GOG has those fixes included, the game is playable and you can easily detect places with light/shadows with no problem.

GOG version also has the mission pack

There is a thread i made here that had a .dll that fixed the same issue in Pandora Tomorrow, some said that it also fixes the problems in SC1, you can try that if you want, I didn't bother cause the GOG version is perfectly playable for me with no problems.