I decided to take my post from the ADOM balance thread and make it into an issue because I actually really like these ideas and don't want to see them disappear in the dustbin of old posts. This suggestion is intended to make spellcasting classes more diverse while making spellcasters in general less overpowered.

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There are many ideas I could name in a minute or two of brainstorming to make the classes more diverse and their gameplays more balanced, or at least exciting. Even classes adept at spellcasting should, for the most part, have problems while trying to do so. Non-wizards should run into random problems as they try to cast spells: spells fizzling and failing to work, wasting a turn just when it would be most critical, for example.

Another idea: divide spells into more categories. Like high magic (Teleportation, Invisibility, etc.), which should be especially difficult to learn and use for anyone but wizards and priests. Death magic (Death Ray, Dispel Undead, etc.) should be difficult to use for most spellcasters but easy for necromancers, while healing magic could be the speciality of healers and priests. Instead of becoming the same overpowered spellcaster, we would see more specialisation: an elementalist may be a master at elemental magic but have problems trying to teleport, while a wizard could dabble at everything while failing to excel at more specialised branches of magic. So not everyone could take Teleportation for granted, nor would everyone be able to spam Acid Ball at orb guardians. [To expand on this: if someone is trying to use a spell they aren't specialising in, they should suffer from serious problems. Spells failing to work is one example; spells firing back at yourself, stats being drained or the caster being stunned/confused are more extreme examples of what could happen if a spell goes wrong.]

Back to necromancers, my pet peeve since I really love the idea of commanding an undead army. Undead summoned by the PC should be much stronger than the average dungeon beastie, since the PC him/herself is also much stronger. Why don't the slaves adjust to the PC's actual level? A level 49 vampire wouldn't be that overpowered; it would still die quickly in an extended BDC trip. Another idea I came up with right now: make the undead much, much stronger, but also make them a finite resource. Force the player to literally channel his/her life essence into conjuration of undead; add artificial aging each time an undead creature is summoned. This could be an absolute value or relative to the PC's life span, I don't know. In exchange, let the player summon special undead, not the boring old dungeon variety. Like an 'ascended lich' that knows a wide variety of spells, not just death ray and confusion but also, for example, Improved Fireball. For lower levels, perhaps a 'greater shadow' that slows and weakens its enemies, or even just a 'skeleton archer' that shoots very powerful missiles for its level.