At first I liked the layout on this one. Judicious slope usage certainly can make basic terrain look much better and interesting. I like how the borders were color-coded with two shades of green, too - dunno if you did this purely for detail or if the following was intended, but I thought it was a pretty smart way to tell the player he's closing in to an edge without forcing him to look around all the time during a fight.
Twilight of the Gods
Not so big on how it actually played out. Most of the time, I ran around looking for the next trigger to flip, and the map is fairly big to cross. At times it felt like there was no visual indications whatsoever of where I was supposed to go.
The fights were... Eh. There are Doom monsters, you shoot them, is how I'd sum it up. Problem being this is a very large map, there's comparatively few monsters in that very large space, and monster pathing isn't so hot with slopes (the first two cyberdemons were actually stuck on those big brown slopes near the start area in my playthrough). If you backpedal to the other end of the map, you could literally go get yourself a drink and be back in time before they catch up to you. It's easy to the point of being tedious, and as I spent more time figuring out which way to go to flip a switch than killing stuff, the main area outstayed its welcome about half of the way in. I didn't even bother picking up the megaspheres.
And then you get to the final area, with stealth revenants and instakill lava. Quite the difficulty spike. Instakills are just bad in general, as far as I'm concerned; and to have them tied to your regular lava texture we're used to take 5 or 10 or 20 damage from? Nah. Lava being merely damaging would be an efficient deterrent (with switches outside of the ring, or moved to the outer wall, so their shots would still hit the player), and a more interesting one at that (you get some extra space if you really need to, but it's going to cost you HP, so it's a balancing act).
The layout is cool but it just feels too big and open for any fight to be interesting as is; anything less than ridiculously spammy with monsters or stingy with resources wouldn't be threatening, and beyond that point the player would just pick somewhere to camp. If there were more stuff obstructing line of sight (even something as simple as 96 pixels high rocks on the roads, or twists and turns in those roads with giant pillar-like structures sitting in the water between), and if ammo caches triggered predictably as the map went on along with just enough monster pressure to make it so you couldn't grab everything at once and just pick a spot and set camp there, this might make it possible to craft some pretty interesting fights with the setting.
As for the final area, seemed like a missed opportunity to me. The fireball switches were by far the coolest part of the whole thing, and it seemed too bad they weren't used more (esp. as you had the whole "switch gods" vibe going since early on). You could have some kind of cool pattern boss fight in there, with switches lightning up (as if activated) in order as they get ready to start shooting.
I know you said it's mostly done so I don't expect you to do any of that, even on the off chance you happened to agree with my perspective. Just indulging myself, thinking of what I'd liked to see. It seemed like a cool concept and I love seeing Doom maps exploring stuff like slopes and the 3D dimension in a way conductive to slightly different gameplay experiences, so I criticize because I care. :)