What annoys me about AD&D spell power, maybe just or mostly in the context of the computer adaptations, is how late in the games so much of the more interesting power comes in. The AD&D logic, from the completely different context of tabletop playing, dictates that strong and impressive spells have to be level 7th, 8th, 9th for wizards (and even then some are not at all impressive, like Energy Drain), level 5th-7th for priests. Up to then players have to make do with illusions, enchantments, Leomund's Secret Lodge, Rope Trick, teleport... Actually, everything from that list and more can be very exciting, but these subtle powers hardly carried over to the PC at all. The most magicky stuff we have until the very concluding chapters of the games is the fireball and the lightning bolt. Whee. When we do get access to a Shape Change, nerfed, of course, it is so late in the day that the party can just blow through anything with the iron fists of fighters alone - whereas in tabletop play, of course, any level of fighter with any + sword would be helpless, running around on the ground while a wizard turned into a dragon to vomit fire on him at leisure or into an ant he'd simply never find.
Overall, I think that AD&D has far too much medium-level magic available, fireball-teleport level, to too many people, but too rarely shows real wonders of magic. Special settings like Al Qadim had to be created just to get out of that rut. The restriction is only more pronounced in the PC games. And this stunted power structure is binding for modders. When we come up with a concept of a spell, say, a flame wave, and actually invent a technique to implement it, what hits us in the face like a wet pancake is the realization that we must make it at least a 7th level. Because it needs to be on par with previous, lame spells. Or else we have to greatly reduce the spell's effect and impression, cut down its damage to squeeze it into level 5, at least, if not 4, so that people actually spend some time using it before game over. But why would a big, gorgeous flame wave do only 1d6 damage per level? So we proceed to shrink down the graphics until it's more like a flame ripple and we don't care for it ourselves any longer - all to fit into this game system's idea of normality and balance.