Yeesh, first you complain that magic in computer games lacks variance and then you cite Diablo of all the choices ? I havent played D3 or D4, so maybe there are more choices. But in D2 you literally would spend all points on one, two, at most maybe three abilities to get good. Really the most simplistic magic in any computer game, ever.
While in Baldur's Gate 2 for example a highlevel spellcaster could have douzens of spells ready, plus various wands as well. Theoretically also scrolls, but since you sadly couldnt scribe scrolls, well that was really only theoretically, since you couldnt create new ones once you spent the ones you could find in the game. Anyway, you could have an enormous amount of spells ready.
And the idea to make spells from general principles is nothing new at all. I already did that in TES3 Morrowind. That magic system is still super simplistic and completely lacked the depth of what BG2 offered.
While BG2 offered for example these spells:
- Friends: Make everybody like you, temporarily
- Sleep: Puts opponents in the area to sleep. Ineffective against higher levels.
- Protection from Evil: Protects against evil attackers. Grants invisibility against demons and devils.
- Protection from Petrification: Protects against being turned into stone
- Sanctuary: Enemies will ignore your existence until you attack them.
- Doom: Make the victim suffer a penalty on all their defenses
- Knock: Open (most) locks (those which can be picked by a thief)
- Entangle: Make an area covered in plants that attempt to grab and hold everyone in this area
- Control Undead: Attempt to control undead in an area
- Melf's Minute Meteors: gain a number of magic projectiles you can throw; hits as a +6 weapon and can thus hit any opponent except for those protected by Protection from Magical Weapons
- Vampire Touch: Touch spell. Drain health from the victim and gain this health for yourself, either for restoring lost hitpoints or gaining temporary hitpoints above your maximum.
- Dispel Magic: Attempt to remove all magic effects in an area
- Remove Magic: like Dispel Magic, except only opponents are affected
- Negative Plane Protection: Protects against energy drain from vampires or spells
- Zone of Sweet Air: Dispel various magic area effects
- Blade Barrier: the caster is surrounded by a ring of blades that attack any enemy close by
- Greater Malison: All enemies in the area gain a penalty to their saves. Only magic resistance gives a chance to avoid this effect.
- Flesh to Stone: turn the victim into a stone statue. The victim can be turned back by the opposite spell Stone to Flesh. Victims do not perceive the passing of time while turned into stone.
- Mirror Image: You create a number of images of yourself. Attackers do not know which one is the real spellcaster, thus they are likely to attack an illusion instead of the real deal.
- Draw Upon Holy Might: Call for the gods to improve your body stats
- Spell Sequencer: Create a sequencer that will cast three spells a once. Player characters can only have one sequencer active at any time. They can also have a Minor Sequencer with is a lesser version.
- Stoneskin: You are protected with a number of layers of stone which disperse when an attack hits them
- Chaotic Commands: Protect the mind of the target from spells attacking the mind
- Dimension Door: Short range teleport
- Hold Monster: Paralyze the victim
- Wizards Eye: Create a magic eye that can explore the area at little danger for the caster; gaze attacks still pass through
- Animate Dead: Create a skeleton summon from a corpse
- Contagion: Attempt to make the target having a disease
- Improved Haste: Target gains twice the number of attacks, and twice the movement speed, and isnt exhausted after the spell expires either.
- Contingency: Cast a spell once a condition is met. Player characters can only have one contingency active at any time. They can also have the higher spell Chain Contingency active, too, which will trigger up to three spells and allows to cast higher spells, too.
- Insect Plague: Enemies in the area are attacked by insects and suffer damage and spell casting failure
- Harm: Touch spell. Reduces the hitpoints of the victim to 1.
- True Sight: See through all illusions
- Resurrection: Raise a fallen ally
- Physical Mirror: Reflects all projectiles back to the attacker
- Disintegrate: Attempt to destroy the target
- Symbol, Stun: Creates a magic trap that will temporarily stun victims
- Protection from Magical Weapons: For a short while, magical weapons cannot harm you
- Gate: open a gate to hell and summon a demon; anyone in the area not under the effect of Protection from Evil will get attacked
- Regeneration: Target will quickly regenerate health over time, for a certain amount of time
- Simulacrum: create a (level lowered) copy of your spellcaster
- Tenser's Transformation: turn the caster into a combat machine. All spellcasting will be disabled. The extra hitpoints gained can effectively work as healing.
- Delayed Blast Fireball: Set a trap in an area that triggers a fireball if anyone gets too close
- Power Word, Kill: Kills the target if they are below a certain hitpoint number. All Power Words have minimal spellcasting time.
- Energy Drain: Attempt to drain two levels from the victim; if the level is reduced to zero, the victim dies. Lost levels can only be restored through corresponding restorative magic.
- Finger of Death: Attempt to slay the victim. If the victim fails the save, they cannot be resurrected anymore either. Undead are not affected by death magic.
- Imprisonment: The victim is transported into a pocket dimension. Can only be freed by the opposing spell Freedom.
- Natures Beauty: The caster is turned into an extremely beautiful creature that will make opponents have to succeed a saving throw or die. If an opponent manages the save, they are merely permanently blinded.
- Spell Trap: Turns spells targeted at the caster into regained spells for the caster
- Wail of the Banshee: Attempt to slay everyone but the caster in the area. Undead are not affected by death magic.
- Wish: wish for certain things to happen. Much more powerful in tabletop than in computer games, of course, because in tabletop you really can make any wish you want.
- Shapeshift: gain the ability to shapeshift into various creatures with different special abilities
- Timestop: halt time for a short while, giving you the ability to cast spells or attack, while your friends and enemies would stay frozen
Etc etc etc etc etc
Compared to that, Diablo is most extremely simple, and Morrowind and Oblivion have still been very simple.