[DaBrain]

I've found my copy of Descent 3 and played a bit.

The engine is quite unusual for the time the game is from. According to Wikipedia it features bumpmapping... well I didn't see any bumpmapping, but I saw the motion blur. Wait... motion blur in 1998?

I didn't notice it back then, but now I think it works quite good for explosions.
The motion blur effect on the stars reminded me a lot of Freespace. Actually it even looked quite a bit better.



How closely related is the FS2 engine to the fusion engine?

[Hunter]

Yes, it has bump mapping. See the small screenshots here? Those were taken in a bump-mapped D3, although the pictures are slightly altered (a grain was added) but it's there. I recommend checking out this mod for Descent 3, which takes it into space combat playable in multiplayer as Team Anarchy.

[Mongoose]

As far as I know, the Fusion engine is essentially unrelated to the FS2 engine; the original FS engine was derived from the engine developed for the first two Descent games, but Descent 3 used a completely new codebase.  The interesting thing about the Fusion engine is that it combined a flight-sim-based engine for outdoor areas with a room-based engine for indoor structures, providing the instantaneous movement between indoors and outdoors that the game allows.