Toyetic Wizardry
Elmcat's post - on how doing magic in a game should feel like something - got me on some points I've been thinking about for a long time.
Zoom out for a minute. The common game idea of a magic user or wizard is just somebody that has a few keys nobody else has to bypass locks most people can't see, or would usually require massively more man/purchasing power to solve.
This is usually pretty strong even with limits on spells and casting times per day, increases in stress, spell backfires, or whatever other mechanics impose consequences for solving big problems. But this means that doing magic is like hitting a button on a big machine that just takes time to recharge. It doesn't make you feel like a fucking wizard.
Most systems make doing magic that simple because it's less likely to eat up playing time - everyone learned from Cyberpunk genre systems that monopolise the GM's time when the hacker dives into gibsonspace. This is a cop out. The real answer is that the effort should be on the part of the person who does the magic, and the referee is only tasked with checking that the result holds up.
The primary state of mind for wizardry is that you know something other people don't. Usually this is a feature of "class", as the knowledge of how to use spells is weighted in favour of the magic user. But it lacks the sauce; the smoky glaze of occultation and creative interpretation.
Doing magic, casting spells, should test you. Like any good tool it's best applied in the hands of someone who can think creatively. It should make you the player feel like you're learning magic. Ars Magicka makes you feel like a wizard. Doing gutter magick in Unknown Armies makes you feel like a wizard. There's some other part of your brain that takes over once you learn how to make magic happen, constantly thinking of how to apply this or that technique to the problem at hand.
If you cast spells by drawing actual physical pictograms that describe what your spell does, but you can only repeat one metaphier in the last three spells you cast at risk of misfire, your thoughts leap to form a symbolic language for effects like "make that guy explode" and "build walls".
Toyetic magic is a puzzle. The rules for that puzzle should be consistent, demand minimal time to determine a real result from a nonfunctional one, apply to multiple situations, and encourage lateral thinking that rewards player knowledge.
Spells should be what happens when you solve the puzzle that being able to cast magic gives you.