In Requiem: Avenging Angel, there are two shortcuts provided to launch the game, one for 3dfx nglide (the default, and recommended shortcut), and one for Direct3D.
In the Direct3D version, there is a game breaking bug at one point of the game. The bug occurs in a hotel area, when you go to speak with the character, Elijah. Speaking with the guard is supposed to trigger a dialogue, which results in opening the doors, however, due to the presence of this bug, the event has a high probability of not occurring. This bug is present in the Direct3D version of the game ONLY.
If you choose to launch the game using Direct3D, we ask that you be mindful of this bug, and switch to the nglide version of the title before entering the aforementioned area to speak with Elijah. Besides this one issue, the Direct3D version of this title is fully playable, which is why it was not removed from our release.