I thought that using the [Chaotic] descriptor would - technically - lead to alignment issues, since it's a chaotic act, plus I tried not to restrict the classes to having to be chaotic. Also it might make some planar travel rather interesting. I also wanted the spells to work with the feats relying on the [Wild] descriptor I made up.
My personal favourite spell is Keys of Chaos, because originally I had it give you a percentage chance equal to your caster level of working, lasting a round a level - so you'd get a bunch of keys and spend aaaaaages trying to get it to work. I changed it to be a little more effective at low levels, unless of course your caster level drops horribly..