Well, the D1 screenshot looks like somewhere from Level 2, only you've got some Z-buffering artifacts there so I'm not too sure. By that time you've only really faced Class-1 and -2 drones and Small Hulks.
The D2 screenshot is from Level 1. You go through the door directly in front of you, kill the PEST, grab the homing missile 4-pack and turn around. Should be a laser near the grating at the bottom of the picture.
The D3 screenshot is from a multiplayer level and I haven't played enough multiplayer to identify the levels that easily.
So, to answer your question... yup, I remember playing them

I bought both games for my new Playstation recently. Plus, I'm the Descent Evangelist in the University's Computer Games Society.