Is it just me, or are these two separate ideas?

1. Randomised spell sets (as in: you don't know which spells your Wizard will start with)
2. A specific spell as you described above (could also have variations for lightning, fire, acid, etc)

Either way, I like both ideas.

Edit: For the 'lightning storm' spell (and its potential variants), another idea would be to simply divide its maximum damage amongst the number of creatures it hits. This would still give the effect of dealing large amounts of damage to a single target (if there's only 1 target in the AOE), but wouldn't be completely useless if you're completely surrounded my baddies.

I'm pretty sure he means spells that are random in nature, rather than a random set of spells. Probably also thinking of things like Ball Lightning, which was a wand with a random direction.

What about:
Healing Surge
-A bolt of healing energy bounces between random targets in AOE sphere, healing both allies and enemies. It heals less and less with each bounce until it fizzles. This would make it a good spell to use to heal your comrades(companions in ADOM could have benefited), or to wreak havoc on a group of Undead without hurting a living caster. It could also help if the caster is badly wounded, but surrounded by fresher enemies as it would heal him, but not aid them much because they aren't wounded.