Starts with all monsters with their backs to you, and you might as well leave it that way and just listen to the music. One big rectangular room with no finish switch. They couldn't even make the rectangle properly - freehand I guess. Kill the monsters if you want, it's easy.
Superb firework display of thousands of fireballs seeming in slow motion because of the vastness - mostly avoidable as they land where you were ages ago; but worth playing just to see it. A HUGE square surrounded by tiers with hundreds of imps and a few others, plus a blockhouse you can enter first to collect ammo. Fighting through the hundreds of monsters when you get onto the tiers is another matter, overwhelming at UV. I cheated to finish so at least I could review. Some HOM bugs.
Insanity, with voodoo dolls (see second screenshot). I get the idea of a shooting gallery if that rocks your boat, but 6000 monsters behind railings- as far as the eye can see, FFS! My PC crawled when I looked towards the invuln spheres (someone said 32 k of them and you can't avoid picking up thousands at a time). In the end I cheated with god mode and no-clipping, and waded in among the chaingunners until I got bored.