What bugs me about D&D magic - and this is true in, as far as I can recall, every other system I've played as well - is how neatly defined all the spells are. They produce exactly this effect, no more and no less. Like, you can use your mastery of the element of fire to create a 6-metre-radius ball of fire that will torch everyone within it, but you can't use it to - y'know - light a campfire, or boil a kettle of water.

This isn't "ridiculous" as such, but it annoys the heck out of me. I guess what really bugs me is that nobody, to the best of my knowledge, has come up with an RPG magic system that really conveys the idea of "mastering" arcane forces, as opposed to just "pulling the levers on someone else's pre-existing machine".