ToME: the Tales of Maj'Eyal

Enemies in pits don't lose the "In Vault" status until you personally see them, unlike enemies in actual vaults who wake up when you open the door. That means you can dump all sorts of AoE overkill into a pit, only to turn a corner and see an entire group of enemies sitting there unscathed because they were out of your LoS. It's even worse if you have Arcane Eye or telepathy to spy on them yourself. I'd suggest making the pit enemies non-invincible, but have them wake up when they take damage or when you see them. Possibly have the awakening chain to adjacent NPCs so the entire pit wakes up at once.

While I agree this makes sense, I think this is the first time I've seen someone complain that out of LoS combat abuse wasn't being enabled enough.

There were super-annoying problems with out of depth shadows being spammed by vault critters, and summons in general could spiral badly out of control if you wake a huge number of critters when you open a door. I'd be careful here.