Just as a test of my AAoS suggestion, here's a couple of save scums. I know it's bordering on "against the site philosophy", but it will give people an idea of the challenge without having to mess around for a couple of levels.
The rules:
#1. You must only use the DB and only THAT DB shotgun.
#2. No master traits or assemblies allowed.
#3. Have fun.
Both saves are just after the Arena on UV AoS (for the DB). I've gone for shottyman first, and you start with a little equipment (too much IMO). The first save is a technician, nearing a level up, so grab Whizzkid and try the challenge as it's intended. The second one is a marine, with BA instead, which will probably make it too easy.
Just remove everything after the word "save" in the filename and dump them in the doomRL directory. A new copy preferably, so you don't sully your player record with evil savescums.
So, way too easy? Way too hard? Way too lame (or not nearly off-the-wall enough for an AA challenege)?
Here's the files. Remember the rules.
EDIT:
After playing around a little with it myself (sounds freaky I know), I've come to the conclusion that it's too bland. Not enough extra fun for an Archangel of * mission. Hard, or rather, very easy at the start, and then very middling in the middle. Pretty damn hard near the end. Most of it is about not getting too far ahead of yourself, not getting too cocky, not going on a rampage. Play with caution most of the time and run hard when you need to. A little too much like AoB, with a reverse scaling (easy->moderately hard compared to hard->moderately hard).
So some more ideas for Archangel of Shotgun. Only a DB still, but you can't use shell boxes. Your shotgun takes two hands to weild. Give cybie a power modded combat shotty and 500 shells, for a weird blastx5/reload/blast dance, constant damage for you at the end. No nukes, Archangels kill in person - not with big, red button. Combat knife on a shotty. This is going to be the biggest god-damned shotty of all, its got a f'ing big blade on the end too (unassemble-able combat knives just reduce a little barrel-item-loss and make it into the shotty beyond all shotties. Gives a reason for brute builds or agility mods on the shotty, bulk still does reload time, power does shot damage. Or both melee/shotty damage for fun).
One player class: AAoSh. Normal stats, UV hardness, dungeon level+5 (no phobos base or arena but maybe a court on lvl1). Starts with an Angel's DB shotgun (takes 3 mods standard, WK still adds 2 to mod limit, max limit 3 per mod type), with normal DB shotgun damage/range/drop-off/fire-time, can melee with it for combat knife damage. Ag mods add to melee accuracy by +2. Gun takes two hands (no prepared slot). Can only use this weapon.
Trait changes:
SoaB: You can deal it, but can you take it? Every 12 damage you take adds +1d3 to your shotgun's damage for the next 5 secs.
EE: If you can see them, by god they'll die. Each level reduces drop-off by 1%.
Int: See no evil. Int(1) is normal. Int(2) gives entire wall layout but no enemy positioning.
Triggerhappy: Renamed as "Face Shot". Each level reduces the enemies natural armour by 1.
Meh, still some work to do and math-sy thinking. It might just work...... Try the trial idea......