So, there are a few elements of ADoM that try to give a feeling of "stealth"... however, short of having some form of invisibility, stealth is mostly just a passive skill in which you hope that monsters won't notice you.

That passive part of Stealth is all well and good, but it seems to me that the game could perhaps incorporate a stealth mode, in which many monsters are much less likely to notice you, given sufficient caution and preparation.

Here's how I'm picturing it: 'a'pplying the Stealth skill should allow the PC to go into a "Stealth Mode", assuming sufficiently high Stealth skill and a defensive Tactic. In Stealth Mode, the PC moves significantly slower (I'm thinking that it should, say, double or triple the movement cost), and cannot attack in the regular melee manner (this brings some more value to the Backstabbing skill, which would be the only regular method for attacking a monster while in Stealth mode). However, the PC also avoids notice much more easily.

But there are restrictions on it all. Metal equipment tends to make noise, which makes stealth difficult. Sources of light (amulets, torches, etc) ruin all attempts at stealth. Casting magic and using crossbows also makes quite a bit of noise, and thus cannot be done while in Stealth mode (bows and slings, and thrown items, are not so noisy to use... however, once the foe knows you're there, stealth won't help you much).

Most of the time, Stealth is used to avoid notice, not to attack. This may be advantageous in cases such as the cavernous level of the puppy cave, the Big Room when first heading for Dwarftown, or the Dwarven Halls (you're not likely to escape notice in the animated forest).

Other skills made easier in conjunction with Stealth: Backstabbing, Pick Pockets, Ventriloquism. Note that Pick Pockets should only work if the foe hasn't noticed the player, which would be an instance of a skill made weaker... but with Stealth, using Pick Pockets would be easier. Confusing a foe that hasn't seen you would also be easier, so Ventriloquism would benefit from Stealth. Backstabbing, as noted before, is the only way to actually attack a foe while in Stealth mode.

Stealth Mode should be activated and deactivated instantaneously, much like tactics. And some monsters should be completely unaffected by stealth mode. A Stealth of 100 should reduce the movement costs of Stealth mode, and should reduce the restrictions on the mode itself, although casting magic and having sources of light should remain out of the question for Stealth mode.