The second half of the Magrathea interlude is summed up in one word: "cramped". The level consists mostly of narrow corridors, usually less than 2 WU in diameter, where monsters snipe at you from a distance, and smallish rooms broken up by pillars and guarded by Compilers. This level is significantly more difficult than Magrathea was, mostly because of the troopers, the lack of room to dodge them, and the fact that there's only 2x health available (and not until you get quite a ways into the level).
Your mission is to shoot out 4 circuits in the central chamber and hit a switch to the north, then high-tail it out of there as the facility fills with lava. The first objective is much easier than it could have been because all the circuits can be reached pretty quickly, removing the need to explore a dangerous set of trooper-filled passages later on that claimed my life more than once. One you complete the second objective, the lower floors of the facility will fill with lava and a set of doors will open which allows complete access to all the rooms on the upper floor. It also opens a final door in the south that lets you fight a super Trooper for the ending terminal.
The terminals on this level have a few nice touches, such as your discovery of the place where the Pfhor hacked the facility's drones to make them hate you, and the way they all turn to static when the lava pours in. But, overall, I can't really think of much to say about this level one way or the other, and I was glad to put it behind me. The first half of Evil is over, and we're about to see some major changes in scenery and gameplay.