Class restrictions
I think there should be some class restrictions implemented into the game. For example, wizards shouldn't be able to run around in things like chain mail or plate mail. They should stay limited to things a bit more suited to their class, like robes and leather armor. I also hate seeing win posts with a wizard running around with say a spear and a shield. A few wizards might use swords but most would be using staffs or pherhaps a dagger/knife, but not a shield and a spear. Also limit the actual number of spells a warrior/fighter can learn. Don't just make casting/learning them harder. Say don't let them learn ball spells or improved fireball, maybe let them have heal light wounds and a couple other weak ones.
I haven't yet finished an ADOM game, but i haven't given up on trying yet either.