I think that the current way wandering monsters work is, to be blunt, pretty
stupid. I can be happily enough butchering a guard, and another guard comes
in, and what does he do? As long as I don't do anything excessively offensive
when he's around, he just watches me kill his comrade.
Therefore, few ideas about what could be done to alleviate things (in
increasing nastiness order):
- Monsters aiding each other even when they wander in if they would've aided
each other when attacked initially (same keyword or whatever the criteria is
now)

- The above, combined with monsters noting combat in neighbor rooms and
wandering there (not very unrealistic, and as general behavior nasty)

- Monsters noting top-N killers of their type and becoming aggressive to them.

Obviously, these kinds of tunes would probably need balancing but they might
be amusing nonetheless (see stun tune for details about similar approach, i.e.
going for more 'fun' gameplay which even currently somewhat downtunes people).

For some reason I'm not too fond of everyone slaughtering tons of small,
totally mindless-seeming monsters.. (And yes, that's what I do too, but with
this kind of tunes, I at least wouldn't be doing it constantly solo but
instead probably in a party, which would be more fun and partying-oriented..)