Perhaps, Fawn mentioned this subject before, but jogging thru Delaras can put a perspective on monsters:
A reminders for her there are some basic monster types:

Archers ~ these tend to be accurate, lots of hit points, very little inclination to move,
very little impact on alerts. They can be ignored to a certain extend unless one must
disable traps/pull levers/stay long times in rooms. However they do contribute to conquest and such.

Soliders ~ these will chase you and have a strong impact on alerts.

Skirmishers ~ kind of a combination of Archers and Soliders, moderate impact on alerts, they
tend to alternate between chasing and backing off to use a ranged weapon, slow to follow,
can become running against a wall to "chase" you instead of finding the door.

Spellcasters ~ various degrees of power, some heal which can lead to attrition battles.
One can be a threat, two can be dangerous, three or more can be deadly. Slow to chase you.
Not sure about the alert impact.

Annoying ~ ozzes, rust monsters, and the like who wear down your equipment. A serious threat
to a solo melee. Can be separated from other monsters by running backwards/forwards as monsters
move at various speeds. The slower ones tend to not contribute quite as much to alert.

Colored boss types ~ various degrees of power, needs to be taken as a possible serious threat.
As they are normally single creatures, their threat value is much higher than alerts caused by them.
Alerts can greatly increase their challenge level.

Basically the faster a creature can move the more likely it will drive the dungeon alert up quicker
to a certain extent. The classic example of this is archers who barely move at all. Watch carefully
at the alert level when archers only are being basically ignored.

Some player's character builds are highly hampered by dungeon alert.
Some players think their character builds can mostly ignore a high alert.
Similar to some characters can survive traps easily while others cannot.

Since D&D version X is a cooperative game, one might...