Also fun that the terminal beyond all the barriers told them to hit 31 switches. I think that one is also accessible in another inside area among the switches that they didn't find, right?
One of my all-time favourite levels - beautiful design with the switches in all the pillars on such a large scale (for Marathon), fun combat with seriously dangerous BoBs, and as it turns out, some interesting stuff with co-op: the solo player could never have seen those barriers dropping from inside the corridor above; could never have returned to the start to find the spawned BoBs until the very end, and could not get back down to hit missed switches without a reload, except for maybe via those stairs down into the lava, but really, that's more of a hassle than reloading :).
The secret through the lava at the end would have been cool with the cheat spawn points; you could have kept teleporting between the first room and the 3x charger, waiting for the lift that usually rises long after you die. I guess the MSG didn't go into enough detail on that one?
And the Tour of Duty wasn't quick enough :(.